JavaScript中for in 和for of的區別

for in 遍歷的是當前索引，不適合遍歷陣列物件，返回的是陣列下標。（適合遍歷物件）

let arr = [
    {name:'張三',age:18},
    {name:'趙四',age:28},
    {name:'王五',age:18}
]
for (const item in arr) {
    console.log(item) // 0, 1, 2
    console.log(arr[item]) // {name:'張三',..},{name:'趙四',..}{name:'王五',..}
}複製程式碼

for of 遍歷的是當前'鍵'值，適合遍歷陣列物件，返回的是陣列單個物件。（適合遍歷陣列物件）

// 例子同上
let arr = [
    {name:'張三',age:18},
    {name:'趙四',age:28},
    {name:'王五',age:18}
]
for (const item of arr) { // 將in 改成 of
    console.log(item) // 0, 1, 2
}複製程式碼