hoisting

问题 I would expect this (reduced for the sake of example) function to run without a hitch, but it fails on account of fn2 is not defined : void function(){ var var1 = fn1(); var var2 = fn2(); function fn1(){}; return function fn2(){}; }(); How does the return statement exclude the function expression for fn2 from hoisting? 回答1: Only a function created with a function declaration is hoisted. The function in return function fn2(){}; is created with a (named) function expression so is not hoisted.

问题 I would expect this (reduced for the sake of example) function to run without a hitch, but it fails on account of fn2 is not defined : void function(){ var var1 = fn1(); var var2 = fn2(); function fn1(){}; return function fn2(){}; }(); How does the return statement exclude the function expression for fn2 from hoisting? 回答1: Only a function created with a function declaration is hoisted. The function in return function fn2(){}; is created with a (named) function expression so is not hoisted.

问题 I came across the following article about variable hoisting in javascript. The article sums up the following three points. 1. All declarations, both functions and variables, are hoisted to the top of the containing scope, before any part of your code is executed. 2. Functions are hoisted first, and then variables. 3. Function declarations have priority over variable declarations, but not over variable assignments. Site Point var showState = function() { console.log("Idle"); }; function

问题 Recently I was confused about javascript hoisting behavior and now I got stuck with that. So, there are two examples. var alpha = 'alpha'; var beta = 'beta'; f(); //beta var f = function f1() { console.log(beta); }; function f() { console.log(alpha); } f(); // alpha The first one is working as expected, because the function declaration overwrite our variable f (with value "undefined") when Javascript is set up the Lexical Environment. But the second gives me a push, that I does not understand

问题 Recently I was confused about javascript hoisting behavior and now I got stuck with that. So, there are two examples. var alpha = 'alpha'; var beta = 'beta'; f(); //beta var f = function f1() { console.log(beta); }; function f() { console.log(alpha); } f(); // alpha The first one is working as expected, because the function declaration overwrite our variable f (with value "undefined") when Javascript is set up the Lexical Environment. But the second gives me a push, that I does not understand

问题 I came across this code: var myVar = 'foo'; (function() { console.log('Original value was: ' + myVar); var myVar = 'bar'; console.log('New value is: ' + myVar); })(); Questions: Is IIFE hoisted to the top before global myVar ? 1a. IF it is, is it executed before global myVar is declared? In IIFE I get undefined first, and bar second. What is the behind the scenes order of execution in IIFE? 回答1: The IIFE is an expression, not a statement, so no it is not hoisted. var myVar inside the IIFE is

问题 I came across this code: var myVar = 'foo'; (function() { console.log('Original value was: ' + myVar); var myVar = 'bar'; console.log('New value is: ' + myVar); })(); Questions: Is IIFE hoisted to the top before global myVar ? 1a. IF it is, is it executed before global myVar is declared? In IIFE I get undefined first, and bar second. What is the behind the scenes order of execution in IIFE? 回答1: The IIFE is an expression, not a statement, so no it is not hoisted. var myVar inside the IIFE is

问题 This question already has answers here : Are variables declared with let or const hoisted? (6 answers) Closed 1 year ago . I'm having a bit of trouble understanding why my code works. I'm expecting a reference error, but everything works fine. My code: const functionA = () => { let bResult = functionB(); console.log("Function A " + bResult); }; const functionB = () => { return "Function B"; }; functionA(); I get this output (no errors); λ node test.js Function A Function B As I understand it,

来源： https://stackoverflow.com/questions/47634568/javascript-temporal-dead-zone

来源： https://stackoverflow.com/questions/63765387/what-is-the-order-of-hoisting-function-declarations-vs-var-declarations-in-js