JavaScript 里的变量和函数提升
变量提升
示例1:
console.log(varName) // output: undefined
var varName = 'i am varName'
console.log(varName) // output: i am varName
由于变量提升，上面等同于
var varName
console.log(varName)
varName = 'i am varName'
console.log(varName)
示例2:
var name = 'Lilei'
(function () {
console.log(name) // output: undefined
var name = 'Hanmeimei'
console.log(name) // output: Hanmeimei
})()
函数提升
示例：
foo() // output: i am foo
varName() // output: Uncaught TypeError: varName is not a function
funcName() // output: Uncaught ReferenceError: funcName is not defined （for ie8, output: i am funcName
function foo() { // function declarations
console.log('i am foo')
}
var varName = function funcName() { // function expression
console.log('i am funcName')
}
函数定义会提升，函数表达式不会（但IE8也会提升）
函数表达式(function expression) 是指
var myFunction = function [name]([param1[, param2[, ..., paramN]]]) {
statements
};
参考资料
http://adripofjavascript.com/blog/drips/variable-and-function-hoisting
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function