3
615 var arr = [];
arr[0] = 'a';
arr[1] = 'b';
arr.foo = 'c';
console.log(arr.length);//2 为什么不是3呢
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arr.foo = 'c';执行后arr仍然是["a", "b"]数据不支持
arr.foo赋值可以使用
arr[2] = 'c'var arr = []; arr[0] = 'a'; arr[1] = 'b'; arr.length = 9; console.log(arr.length);//9 console.log(arr[3]);//undefined