JavaScript，数组A长度为0但A[key]有值

Question

这是代码

var A = [];
A['key1'] = 'apple';
console.log(A.length);
console.log(A['key1']);

日志中的 A.length 为 0....但我就是不明白，显然 A['key1'] 的值为 'apple'。为什么A.length为0？

Answer 1

你定义的A是数组。数组不是键值对，对象只有键值对

检查 console.log A 它仍然是空的

 var A = [];
    A['key1'] = 'apple';//its not added because is a array
    console.log(A);    
    console.log(A.length);
    

如果您需要添加键值对 将A 定义为对象。并使用Object.keys(A) 查找长度.它将创建对象键数组

var A = {};
    A['key1'] = 'apple';
    console.log(A);    
    console.log(Object.keys(A).length);
    console.log(A.key1.length)

最好看 Difference between an array and an object?