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JS Loops Example (for...in, for...of, forEach(), entries(), keys(), values())
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| /** | |
| * Array Looping | |
| */ | |
| const arr = ['foo']; | |
| // A for...in loop will return the key... | |
| // @see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in | |
| for (const key in arr) { | |
| console.log(key); | |
| } | |
| // A for...of loop will return the value... | |
| // @see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of | |
| for (const val of arr) { | |
| console.log(val); | |
| } | |
| // A forEach loop can return the value, key and array... | |
| // @see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach | |
| arr.forEach((val) => console.log(val)); | |
| arr.forEach((val, key) => console.log(val, key)); | |
| arr.forEach((val, key, all) => console.log(val, key, all)); | |
| // Array.entries() will return the key and value... | |
| for (const [key, val] of arr.entries()) { | |
| console.log(key, val); | |
| } | |
| // Array.keys() and Array.values() will return an iterator... | |
| console.log(arr.keys()); | |
| console.log(arr.values()); | |
| /** | |
| * Object Looping | |
| */ | |
| const obj = { foo: 'bar' }; | |
| // A for...in loop will return the key... | |
| for (const key in obj) { | |
| console.log(key); | |
| } | |
| // A for...of loop doesn't work... | |
| // for (const val of obj) { | |
| // console.log(key); | |
| // } | |
| // A forEach loop doesn't work either... | |
| // obj.forEach((val) => console.log(val)); | |
| // obj.forEach((val, key) => console.log(val, key)); | |
| // obj.forEach((val, key, all) => console.log(val, key, all)); | |
| // Object.entries() will return the key and value... | |
| for (const [key, val] of Object.entries(obj)) { | |
| console.log(key, val); | |
| } | |
| // Object.keys() and Object.values() will return the keys and values... | |
| console.log(Object.keys(obj)); | |
| console.log(Object.values(obj)); |
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