undefined 和 is not defined
//1
console.log(a); // is not defined
//2
var a;
console.log(a); //undefined
//3
console.log(a); //undefined
var a = 10;相关文章：
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//1
console.log(a); // is not defined
//2
var a;
console.log(a); //undefined
//3
console.log(a); //undefined
var a = 10;相关文章：