js迴圈遍歷
阿新 • • 發佈:2022-04-13
1. for 迴圈 arr/str
let cars = ["BMW", "Volvo", "Saab", "Ford"];
for (var i = 0; i < cars.length; i++) {
console.log(cars[i]);
}
例:
for (;cars[i];)
{
document.write(cars[i] + "<br>");
i++;
}
3. while 迴圈 arr
let i = 0,txt = '';
while (i < 5)
{
txt = txt + "The number is " + i + "<br>";
console.log(txt);
i++;
}
例:
while (cars[i])
{
document.write(cars[i] + "<br>");
i++;
}
5. foreach 迴圈 arr (不能響應continue,break,return)
cars.forEach(element => {
console.log(element)
});
cars.forEach((item, index, arr) => {
console.log(item,index,arr) //內容,下標,元素組
});
7. for...of 迴圈 arr/map/set/str
for (let iterator of cars) {
console.log(iterator)
}
2. for/in 迴圈 arr,obj let cars = ["BMW", "Volvo", "Saab", "Ford"]; let cars = {fname:"Bill",lname:"Gates",age:56}; for(let key in cars){ console.log(key,cars[key]) }
4. do/while 迴圈 arr let i = 0,txt = ''; do { txt = txt + "The number is " + i + "<br>"; console.log(txt); i++; } while (i < 5);
6. map 迴圈 arr let cars = ['arm','leg']; let array = cars.map((item,index,arr)=>{ return item + 2; }) console.log(array)
8. filter 迴圈 arr (資料過濾返回新陣列) let arr = cars.filter(item=>{ return item == 'arm';// return item.age > 10 ; }); console.log(arr)
9. every 迴圈 arr (陣列全部驗證,所有都符合返回true) let result = cars.every((item,index,arr)=>{ return item > 3; })
10. some 迴圈 arr (陣列全部驗證,所有都符合返回true) let result = cars.some((item,index,arr)=>{ return item > 3; })
11. reduce 迴圈 arr (資料之間的運算,從左到右,10是initialValue初始值,預設是陣列第一項) let result = cars.reduce((initialValue,currentValue,index,arr)=>{ return initialValue + currentValue; },10)
12. reduceRight 迴圈 arr(與reduce相同,執行順序相反)
13. find 迴圈 arr (與filter相同,但只找到符合條件的第一項,沒找到返回undefind)
14. findIndex 迴圈 arr (與find相同,但找下標)
15. keys、values、entries arr (返回遍歷器物件,用for...of進行遍歷) keys 返回元素索引,values 返回元素本身,entries 返回元素和下標 for(let cc of arr.keys/values()){ console.log(cc); } for(let [ind,ele] of arr.entries()){ console.log(cc); }