for-of-loop

问题 I accidentally witnessed that this causes an error in V8 (Chrome, Node.js, etc): for (let val of Symbol()) { /*...*/ } TypeError: Symbol is not a function or its return value is not iterable It appears that any other non-iterable value (including a function) causes another error: for (let val of function () { throw 'never called' }) { /*...*/ } TypeError: (intermediate value) is not iterable As the reference states, the error is specific to Chrome: TypeError: 'x' is not a function or its

问题 I accidentally witnessed that this causes an error in V8 (Chrome, Node.js, etc): for (let val of Symbol()) { /*...*/ } TypeError: Symbol is not a function or its return value is not iterable It appears that any other non-iterable value (including a function) causes another error: for (let val of function () { throw 'never called' }) { /*...*/ } TypeError: (intermediate value) is not iterable As the reference states, the error is specific to Chrome: TypeError: 'x' is not a function or its

问题 When using a for of loop, both of these are allowed and work: const numbers = [1,2,3]; // works for(let number of numbers) { console.log(number); } // also works for(const number of numbers) { console.log(number); } I always use const since I annot fanthom changing the number variable in any context, but when I see a for...of loop in other people's code, it often uses let . Maybe there's a drawback to const that I didn't see? Browser bugs? Why use const and when to use let in for...of loops?

问题 I recently came across this code: for (const temp of [1,2]) { // do something } I thought that it'd be better to use let declaration for temp because this way the variable would be declared only once. However, I also ran this example as well as the version with let through babel and this is what I see: for (const p of [1,2]) { } for (let s of [1,2]) { } became: for (var _i = 0, _arr = [1, 2]; _i < _arr.length; _i++) { var p = _arr[_i]; } for (var _i2 = 0, _arr2 = [1, 2]; _i2 < _arr2.length;

问题 I recently came across this code: for (const temp of [1,2]) { // do something } I thought that it'd be better to use let declaration for temp because this way the variable would be declared only once. However, I also ran this example as well as the version with let through babel and this is what I see: for (const p of [1,2]) { } for (let s of [1,2]) { } became: for (var _i = 0, _arr = [1, 2]; _i < _arr.length; _i++) { var p = _arr[_i]; } for (var _i2 = 0, _arr2 = [1, 2]; _i2 < _arr2.length;

问题 I am building an Array with const myCanvas = documen.getElementsByTagName('canvas') that it's actually working. It returns me something like this: images: [ 0: canvas, 1: canvas, 2: canvas ] This is for a Typescript project, I want to iterate this Array and transform each image in order to log it. Like this: for (const image of myCanvas) { console.log(canvas.toDataURL()); } (I am not using foreach because it doesn't works with HTMLCollectionOf type) I need to iterate the HTMLCollection that

问题 I have seen that since ECMA 6 we can use for...of instead of the traditionnal for loop: for( let i = 0 ; i < arr.length ; i++ ) { var elm = arr[i]; // do stuff } VS for( let elm of arr ) { // do stuff } Has you see the second one is lot more readable, simple and maintainable! I just wonder how performant the second syntax is as I need to use it a lot in a render loop (60 times per seconds) for a game. Have you got a clue ? 回答1: The first one (the standard for-loop) performs much better

问题 Currently I am trying to build a simple sidenavigation that appears/disappears whenever one of the "toggleSidenav" buttons is clicked (there are multiple). It seemed to work fine when testing with Firefox and Chrome but today when I tried to open my page with Safari (desktop and mobile version) the buttons didn't do anything. The problem seems to be the for-of-loop I used but checking the reference of the for...of, Safari should support it. My code: for (var btn of document

问题 Currently I am trying to build a simple sidenavigation that appears/disappears whenever one of the "toggleSidenav" buttons is clicked (there are multiple). It seemed to work fine when testing with Firefox and Chrome but today when I tried to open my page with Safari (desktop and mobile version) the buttons didn't do anything. The problem seems to be the for-of-loop I used but checking the reference of the for...of, Safari should support it. My code: for (var btn of document

问题 Currently I am trying to build a simple sidenavigation that appears/disappears whenever one of the "toggleSidenav" buttons is clicked (there are multiple). It seemed to work fine when testing with Firefox and Chrome but today when I tried to open my page with Safari (desktop and mobile version) the buttons didn't do anything. The problem seems to be the for-of-loop I used but checking the reference of the for...of, Safari should support it. My code: for (var btn of document