hoisting

问题 function g () { var x; function y () {}; var z; } I would like to know exactly what order the above code becomes when hoisted. Theory 1: Order between var s and function s remains as-is: function g () { var x; function y () {}; var z; } Theory 2: var s come before function s: function g () { var x; var z; function y () {}; } Theory 3: function s come before var s: function g () { function y () {}; var x; var z; } Which theory is correct? 回答1: Functions are hoisted first, then variable

问题 As I understand it, the IIFE pattern is a work around to the fact that ES5 and below do not have a way to create block scopes. By wrapping everything in a function and immediately invoking it, we can create a scope. Now that let and const will gain support by more the browsers, does this reduce the need for something like the IIFE pattern? 回答1: Yes, blocks are going to replace IEFEs, as soon as block-scoped declarations (functions, let/const/class) become widely adopted. You need a scope, e.g

问题 Why does JavaScript hoist variables? What was the rationale of the designers when they decided to implement hoisting? Are there any other popular languages that do this? Please provide relevant links to documentation and/or records. 回答1: As Stoyan Stefanov explains in "JavaScript Patterns" book, the hoisting is result of JavaScript interpreter implementation. The JS code interpretation performed in two passes. During the first pass, the interpreter processes variable and function declarations

问题 alert(myVar1); return false; var myVar1; Above code throws error in IE, FF and Opera stating that return statement has to come in the function. But it works (shows undefined ) in Safari and Chrome. The above code has been written in global scope. Outside all the functions. Any reason? 回答1: In javaScript Variables are moved to the top of script and then run. So when you run it will do var myVar1; alert(myVar1); return false; This is because javascript doesnt really have a true sense of lexical

问题 I have been playing with ES6 for a while and I noticed that while variables declared with var are hoisted as expected... console.log(typeof name); // undefined var name = \"John\"; ...variables declared with let or const seem to have some problems with hoisting: console.log(typeof name); // ReferenceError let name = \"John\"; and console.log(typeof name); // ReferenceError const name = \"John\"; Does this mean that variables declared with let or const are not hoisted? What is really going on

问题 I just read a great article about JavaScript Scoping and Hoisting by Ben Cherry in which he gives the following example: var a = 1; function b() { a = 10; return; function a() {} } b(); alert(a); Using the code above, the browser will alert \"1\". I\'m still unsure why it returns \"1\". Some of the things he says come to mind like: All the function declarations are hoisted to the top. You can scope a variable using function. Still doesn\'t click for me. 回答1: Function hoisting means that