for (var i = 0; i < list.length; i++) {
//循環體
}
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最基礎的循環也有優化的空間:整個循環中數組的長度是不會改變的javascript
for (var i = 0, len = list.length; i < len; i++) {
//循環體
}
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for (var key in obj) {
//循環體
}
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var data = [1, 2, 3, 4, 5];
data.forEach((item, index, list) => {
list[index] = item + 1;
})
console.log(data); // =>[2, 3, 4, 5, 6]
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var data = [1, 2, 3];
var b = data.map((item) => {
return item * item;
})
console.log(b); // =>[1, 4, 9]
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const arr = ['red', 'green', 'blue'];
for(let v of arr) {
console.log(v); // red green blue
}
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2.獲取數組的鍵 值 鍵值對。 keys()是對鍵名的遍歷、values()是對鍵值的遍歷,entries()是對鍵值對的遍歷。java
const arr = ['a', 'b'];
for (let index of arr.keys()) {
console.log(index); // 0 1
}
for (let elem of arr.values()) {
console.log(elem); // 'a' 'b'
}
for (let [index, elem] of arr.entries()) {
console.log(index, elem); // 0 "a" 1 "b"
}
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