let should be be used for any variable expecting to be reassigned. if the boolean is false 3 months and 1 day will result in a difference of 3 months. Nice. Because this answer already confused it for variables, not functions. The other difference between var and let is that the latter can only be accessed after its declaration is reached (see temporal dead zone). So you have to take account for timezone offset, which you can do so by adding The difference is that a var can be re-assigned to whereas a val cannot. And this answer itself is an indication that the use of const to define a function is not a readability enhancement and in fact a readability regression in modern JS. Using Babel will transform async/await to generator function and using forEach means that each iteration has an individual generator function, which has nothing to do with the others. let difference = arr1 .filter(x => !arr2.includes(x)) .concat(arr2.filter(x => !arr1.includes(x))); This way, you will get an array containing all the elements of arr1 that are not in arr2 and vice-versa The default behavior only counts whole months, e.g. For-of loop lets you iterate array elements. let startTime = new Date(timeStamp1); let endTime = new Date(timeStamp2); to get the difference between the dates in seconds -> let timeDiffInSeconds = Math.floor((endTime - startTime) / 1000); but this porduces results in utc(for some reason that i dont know). Checking for properties of the object instance (not including inherited properties) *2021 - Using the new method ***Object.hasOwn() as a replacement for Object.hasOwnProperty() Object.hasOwn() is intended as a replacement for Object.hasOwnProperty() and is a new method available to use (yet still not fully supported by all browsers like safari yet but soon will be) let difference = arr1 .filter(x => !arr2.includes(x)) .concat(arr2.filter(x => !arr1.includes(x))); This way, you will get an array containing all the elements of arr1 that are not in arr2 and vice-versa @Phil_1984_ This answer and top voted answer are very different. As some of the answers noted though, your implementation can be much simpler if you actually have DSV or TSV file, as they disallow the use of the record and field separators in the values. It just calls the function for each array element and then its done. let should be be used for any variable expecting to be reassigned. An efficient way to loop over an Array is the built-in array method .map(). In the first example, the whole function declaration is hoisted. The mutability, or otherwise of whatever is actually assigned, is a side issue: import collection.immutable import collection.mutable var m = immutable.Set("London", "Paris") m = immutable.Set("New York") //Reassignment - I have change the "value" at m. Whereas: Just like const the let does not create properties of the window object when declared globally (in the top-most scope). 3819. While let and const are block-scoped and not function scoped as var it shouldnt make a difference while discussing their hoisting behavior. @Spig: interesting, tried it on Firefox and it worked. OP's question was how to sort an object literal. so they will be executed independently and has no context of next() with others. Multiple ways using ES6 Using spread operator () and keys method [ Array(N).keys() ].map( i => i+1); Fill/Map Array(N).fill().map((_, i) => i+1); Array.from Destructuring assignment lets you extract values from an array or an object and assign them to variables. using .setUTCHours() it would be possible to actually set dates in UTC-time, which would allow you to use UTC-times throughout the system.. You cannot set it using UTC in the constructor though, unless you specify a date-string. So, forEach doesnt actually return anything. So, forEach doesnt actually return anything. An efficient way to loop over an Array is the built-in array method .map(). let difference = arr1 .filter(x => !arr2.includes(x)) .concat(arr2.filter(x => !arr1.includes(x))); This way, you will get an array containing all the elements of arr1 that are not in arr2 and vice-versa This code is not yet tested thoroughly, but anyone is welcome to use it. Const: If the value you have is computed at runtime (new DateTime.now(), for example), you can not use a const for it.However, if the value is known at compile time (const a = 1;), then you should use const over final.There are 2 other large differences between const and final.Firstly, if you're using const inside a class, you have to Checking for properties of the object instance (not including inherited properties) *2021 - Using the new method ***Object.hasOwn() as a replacement for Object.hasOwnProperty() Object.hasOwn() is intended as a replacement for Object.hasOwnProperty() and is a new method available to use (yet still not fully supported by all browsers like safari yet but soon will be) Here's a function that accurately provides the number of months between 2 dates. For a 1-dimensional array it would look like this: function HandleOneElement( Cuby ) { Cuby.dimension Cuby.position_x } cubes.map(HandleOneElement) ; // the map function will pass each element And this answer itself is an indication that the use of const to define a function is not a readability enhancement and in fact a readability regression in modern JS. The Date object will do what you want - construct one for each date, then compare them using the >, <, <= or >=.. How do I use JavaScript to calculate the day of the year, from 1 - 366? Top voted answer says you can't, then gives a workaround by storing sorted keys in an array, then iterating and printing key value pairs from the sorted array. This includes within a for loop. In the first example, the whole function declaration is hoisted. 3 months and 1 day will result in a difference of 3 months. OP's question was how to sort an object literal. Actually, a simple for() loop also works because the iterations are also in one single Array.forEach executes a provided function once per array element.. You could also do that: In package.json: "scripts": { "cool": "./cool.js" } In cool.js:. Use const and let. For example: January 3 should be 3. using .setUTCHours() it would be possible to actually set dates in UTC-time, which would allow you to use UTC-times throughout the system.. You cannot set it using UTC in the constructor though, unless you specify a date-string. The Date object will do what you want - construct one for each date, then compare them using the >, <, <= or >=.. So, what does this mean? I think it falls into a grey area in the specification of how getMinutes() should work. The mutability, or otherwise of whatever is actually assigned, is a side issue: import collection.immutable import collection.mutable var m = immutable.Set("London", "Paris") m = immutable.Set("New York") //Reassignment - I have change the "value" at m. Whereas: Note: You can't do import { A }; when you did const A = 42; export default A; This might seem weird, and may break your imports when refactoring from named to default exports (unless you remove the curly braces). var abc = function() {}; The main difference is how they are hoisted (lifted and declared). This is (essentially) incorrect in most cases: var array = []; array["Main"] = "Main page"; That creates a non-element property on the array with the name Main.Although arrays are objects, normally you don't want to create non-element properties on them. ). At this time, for each recursion, the array has to be iterated in all his elements when filtered by x (the first element). And this answer itself is an indication that the use of const to define a function is not a readability enhancement and in fact a readability regression in modern JS. In short: Read the files using the HTML5 FileReader API with .readAsArrayBuffer; Create a Blob with the file data and get its url with window.URL.createObjectURL(blob); Create new Image element and set it's src to the file blob url Javascript re-assign let variable with destructuring. @Craig - You can't use const in a for loop in most cases (though you can in some), because of the "increment" part of the loop. The syntax is for (const element of array) (we can replace const with var or let, but it's better to use const if we don't intend to modify element). @Craig - You can't use const in a for loop in most cases (though you can in some), because of the "increment" part of the loop. To put it simply: let elemRectangle = elem.getBoundingClientRect() // The function returns the largest integer less than or equal to a given number. Ask Question Asked 7 years, 10 months ago. On for (let i = 0; i < 10; ++i) for instance, after an iteration and the test, when doing the ++i part the engine creates the new i for the new iteration, assigns it the value the old i had, and then does the increment part: ++i, which modifies the new i. The default behavior only counts whole months, e.g. Const: If the value you have is computed at runtime (new DateTime.now(), for example), you can not use a const for it.However, if the value is known at compile time (const a = 1;), then you should use const over final.There are 2 other large differences between const and final.Firstly, if you're using const inside a class, you have to CSV, on the other hand, can actually have The other difference between var and let is that the latter can only be accessed after its declaration is reached (see temporal dead zone). Using Babel will transform async/await to generator function and using forEach means that each iteration has an individual generator function, which has nothing to do with the others. What is the difference between "let" and "var"? Because this answer already confused it for variables, not functions. Javascript re-assign let variable with destructuring. I have an implementation as part of a spreadsheet project.. This is (essentially) incorrect in most cases: var array = []; array["Main"] = "Main page"; That creates a non-element property on the array with the name Main.Although arrays are objects, normally you don't want to create non-element properties on them. Just like const the let does not create properties of the window object when declared globally (in the top-most scope). CSV, on the other hand, can actually have Object destructuring without var, let or const. I think it falls into a grey area in the specification of how getMinutes() should work. Here's a function that accurately provides the number of months between 2 dates. using .setUTCHours() it would be possible to actually set dates in UTC-time, which would allow you to use UTC-times throughout the system.. You cannot set it using UTC in the constructor though, unless you specify a date-string. so they will be executed independently and has no context of next() with others. This includes within a for loop. if the boolean is false An efficient way to loop over an Array is the built-in array method .map(). For this reason, let declarations are commonly regarded as non-hoisted. Short explanation goes like this: "" spread operator deconstructs the object literal and adds it to "obj" e.g. Ask Question Asked 7 years, 10 months ago. 46. 46. const should be used for ~95% of cases. This is an addition to dmd733's answer.I fixed the bug with Day duration (well I hope I did, haven't been able to test every case). Short explanation goes like this: "" spread operator deconstructs the object literal and adds it to "obj" e.g. Actually, a simple for() loop also works because the iterations are also in one single let permet de dclarer des variables dont la porte est limite celle du bloc dans lequel elles sont dclares. let should be be used for any variable expecting to be reassigned. Object destructuring without var, let or const. Just figure out the difference in seconds (don't forget JS timestamps are actually measured in milliseconds) and decompose that value: // get total seconds between the times var delta = Math.abs(date_future - date_now) / 1000; // calculate (and subtract) whole days var days = Math.floor(delta / 86400); delta -= days * 86400; // calculate (and subtract) whole hours var Just figure out the difference in seconds (don't forget JS timestamps are actually measured in milliseconds) and decompose that value: // get total seconds between the times var delta = Math.abs(date_future - date_now) / 1000; // calculate (and subtract) whole days var days = Math.floor(delta / 86400); delta -= days * 86400; // calculate (and subtract) whole hours var What is the difference between "let" and "var"? How do I get the difference between 2 dates in full days (I don't want any fractions of a day) var date1 = new Date('7/11/2010'); var date2 = new Date('12/12/2010'); var diffDays = date2.getDate() - complete, you will access your Teams at stackoverflowteams.com, and they will no longer appear in the left sidebar on stackoverflow.com. I think it falls into a grey area in the specification of how getMinutes() should work. This includes within a for loop. Note: You can't do import { A }; when you did const A = 42; export default A; This might seem weird, and may break your imports when refactoring from named to default exports (unless you remove the curly braces). 3819. @Craig - You can't use const in a for loop in most cases (though you can in some), because of the "increment" part of the loop. let viewportX = e.clientX let viewportY = e.clientY // Viewport-relative position of the target element. You could also do that: In package.json: "scripts": { "cool": "./cool.js" } In cool.js:. Just like const the let does not create properties of the window object when declared globally (in the top-most scope). That is, O(position) instead of Short explanation goes like this: "" spread operator deconstructs the object literal and adds it to "obj" e.g. For a 1-dimensional array it would look like this: function HandleOneElement( Cuby ) { Cuby.dimension Cuby.position_x } cubes.map(HandleOneElement) ; // the map function will pass each element Array.map creates a new array with the results of calling a provided function on every element in this array.. I also quickly added a String property to the result that holds the general time passed (sorry for the bad nested ifs!! This is (essentially) incorrect in most cases: var array = []; array["Main"] = "Main page"; That creates a non-element property on the array with the name Main.Although arrays are objects, normally you don't want to create non-element properties on them. Just figure out the difference in seconds (don't forget JS timestamps are actually measured in milliseconds) and decompose that value: // get total seconds between the times var delta = Math.abs(date_future - date_now) / 1000; // calculate (and subtract) whole days var days = Math.floor(delta / 86400); delta -= days * 86400; // calculate (and subtract) whole hours var In the second example only the var 'abc' is hoisted, its value (the function) will be undefined, and the function itself remains at the position that it is declared. That is, O(position) instead of So whatever you return within that called function is simply discarded. This will be O(n) where n is the number of objects in array and m is the number of unique values. @Phil_1984_ This answer and top voted answer are very different. Checking if a key exists in a JavaScript object? To put it simply: The syntax is for (const element of array) (we can replace const with var or let, but it's better to use const if we don't intend to modify element). Here are some of my though that may help someone latter. The atob function will decode a Base64-encoded string into a new string with a character for each byte of the binary data.. const byteCharacters = atob(b64Data); Each character's code point (charCode) will be the value of the byte. ). The other difference between var and let is that the latter can only be accessed after its declaration is reached (see temporal dead zone). The difference is that a var can be re-assigned to whereas a val cannot. The export default A only refers to the value 42 So, what does this mean? So you have to take account for timezone offset, which you can do so by adding CSV, on the other hand, can actually have So, forEach doesnt actually return anything. ES6 introduced JavaScript developers the let and const keywords. @BenWainwright: Maintaining a BiMap or equivalent (Alethess answer) is often the efficient O(1) approach to the broader problem, but even for one-offs its at least possible to iterate with for in and break upon finding a match, rather than creating an entire array of keys ahead of time, leading to a best case better than the worst case. It makes it so the variable reference can't change, thus array, object, and DOM node properties can change and should likely be const. In the first example, the whole function declaration is hoisted. @BenWainwright: Maintaining a BiMap or equivalent (Alethess answer) is often the efficient O(1) approach to the broader problem, but even for one-offs its at least possible to iterate with for in and break upon finding a match, rather than creating an entire array of keys ahead of time, leading to a best case better than the worst case. so they will be executed independently and has no context of next() with others. For a symmetric difference, you can do:. Top voted answer says you can't, then gives a workaround by storing sorted keys in an array, then iterating and printing key value pairs from the sorted array. Note: You can't do import { A }; when you did const A = 42; export default A; This might seem weird, and may break your imports when refactoring from named to default exports (unless you remove the curly braces). 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