For...In loops 可以遍歷一個(gè)object的 keys.
const shark = {
species: "great white",
color: "white",
numberOfTeeth: Infinity
}
// Print property names of object
for (attribute in shark) {
console.log(attribute);
}
Output :
species
color
numberOfTeeth
For...Of Loop is a new feature of ES6.
可用于遍歷一個(gè)可迭代的對象的值，比如array, string
// Initialize array of shark species
let sharks = [ "great white", "tiger", "hammerhead" ];
// Print out each type of shark
for (let shark of sharks) {
console.log(shark);
}
Output :
great white
tiger
hammerhead
一個(gè)比較：
const str1 = "asdf"
for (const element of str1) {
console.log(element);
}
console.log("------------");
const str2 = "asdf"
for (const element in str2) {
console.log(element);
}
Output:
"a"
"s"
"d"
"f"
"0"
"1"
"2"
"3"
var arr = [3, 5, 7];
arr.foo = "hello";
for (var i in arr) {
console.log(i); // logs "0", "1", "2", "foo"
}
for (var i of arr) {
console.log(i); // logs "3", "5", "7"
}
Another distinction is that for..in operates on any object; it serves as a way to inspect properties on this object. for..of on the other hand, is mainly interested in values of iterable objects. Built-in objects like Map and Set implement Symbol.iterator property allowing access to stored values.
