js 对象循环遍历

let obj = { a: 1, b: 2, c: 3, d: 4};
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1 for in

for (let key in obj) {
    // key: a, b, c, d
    console.log(obj[key]); // 1, 2, 3, 4
}
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可以使用break， continue，和正常for 循环一样

2 Object,keys(obj)，返回key组成的数据，再遍历

Object.keys(obj).map(key => { // ["a", "b", "c", "d"]
    console.log(obj[key]); // 1, 2, 3, 4
})
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3 Object.getOwnPropertyNames(obj)，返回key组成的数据，再遍历

Object.getOwnPropertyNames(obj).map(key => { // ["a", "b", "c", "d"]
    console.log(obj[key]); // 1, 2, 3, 4
})
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4 Object.entries(obj)，返回可枚举属性的键值对数组

for (let [key, value] of Object.entries(obj)) { // [["a", 1], ["b", 2], ["c", 3], ["d", 4]]
    console.log(key, value); // a 1 b 2 c 3 d 4
}
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