1，变量
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</head><body><script>// 1.把所有var声明的变量提升到 当前作用域的最前面// 2.只提升声明，不提升赋值// var num// console.log(num)//undefined// num = 10// console.log(num)//10function fn() {console.log(num)//未定义var num = 10}</script>
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2，函数提升
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<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><script>// 1.把所有var声明的变量提升到 当前作用域的最前面// 2.只提升声明，不提升赋值// var num// console.log(num)//undefined// num = 10// console.log(num)//10// function fn() {// console.log(num)//未定义// var num = 10// }fun()var fun = function () {console.log('函数表达式')}// 这里只针对变量名fun做了声明而非函数体// 所以会报错</script>
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