JS——预解析

1、排查语法错误

<script>
    console.log(1;
</script>

2、变量提升和函数整体提升

<script>
    console.log(n1);
</script>

<script>
    console.log(n1);
    var n1 = 1;
</script>

3、变量提升只提升变量名不提升变量的值