解构使得将数组中的值或对象中的属性解包为不同的变量成为可能。
优点
- 使代码简洁且更具可读性。
- 我们可以轻松避免重复的解构表达式。
一些用例
- 从对象、数组中获取变量值。
let array = [1, 2, 3, 4, 5]; let [first, second, ...rest] = array; console.log(first, second, rest); //expected output: 1 2 [3,4,5] let objectfoo = { foo: 'foo' }; let { foo: newvarname } = objectfoo; console.log(newvarname); //expected output: foo // nested extraction let objectfoobar = { foo: { bar: 'bar' } }; let { foo: { bar } } = objectfoobar; console.log(bar); //expected output: bar
- 仅更改对象中所需的属性。
let array = [ { a: 1, b: 2, c: 3 }, { a: 4, b: 5, c: 6 }, { a: 7, b: 8, c: 9 }, ]; let newarray = array.map(({ a, ...rest }, index) => ({ a: index + 10, ...rest, })); console.log(newarray); /* expected output: [ { "a": 10, "b": 2, "c": 3 }, { "a": 11, "b": 5, "c": 6 }, { "a": 12, "b": 8, "c": 9 } ]*/
- 将参数中的值提取到独立变量中。
// object destructuring: const objectdestructure = ({ property }: { property: string }) => { console.log(property); }; objectdestructure({ property: 'foo' }); //expected output: foo // array destructuring: const arraydestructure = ([item1, item2]: [string, string]) => { console.log(item1 , item2); }; arraydestructure(['bar', 'baz']); //expected output: bar baz // assigning default values to destructured properties: const defaultvaldestructure = ({ foo = 'defaultfooval', bar, }: { foo?: string; bar: string; }) => { console.log(foo, bar); }; defaultvaldestructure({ bar: 'bar' }); //expected output: defaultfooval bar
- 从对象中获取动态键值。
const obj = { a: 1, b: 2, c: 3 }; const key = 'c'; let { [key]: val } = obj; console.log(val); //expected output: 3
- 交换值。
const b = [1, 2, 3, 4]; [b[0], b[2]] = [b[2], b[0]]; // swap index 0 and 2 console.log(b); //expected output : [3,2,1,4]
- 获取对象的子集。
const obj = { a: 5, b: 6, c: 7 }; const subset = (({ a, c }) => ({ a, c }))(obj); console.log(subset); // expected output : { a: 5, c: 7 }
- 进行数组到对象的转换。
const arr = ["2024", "17", "07"], date = (([year, day, month]) => ({year, month, day}))(arr); console.log(date); /* expected output: { "year": "2024", "month": "07", "day": "17" } */
- 在函数中设置默认值。
function somename(element, input, settings={i:"#1d252c", i2:"#fff", ...input}){ console.log(settings.i); console.log(settings.i2); } somename('hello', {i: '#123'}); somename('hello', {i2: '#123'}); /* expected output: #123 #fff #1d252c #123 */
- 获取数组长度、函数名称、参数数量等属性。
let arr = [1,2,3,4,5]; let {length} = arr; console.log(length); let func = function dummyfunc(a,b,c) { return 'a b and c'; } let {name, length:funclen} = func; console.log(name, funclen); /* expected output : 5 dummyfunc 3 */
- 组合数组或对象。
//combining two arrays const alphabets = ['A','B','C','D','E','F']; const numbers = ['1','2','3','4','5','6']; const newArray = [...alphabets, ...numbers] console.log(newArray); //expected output: ['A','B','C','D','E','F','1','2','3','4','5','6'] //combining two objects const personObj = { firstname: "John", lastname: "Doe"}; const addressObj = { city: "some city", state: "some state" }; const combinedObj = {...personObj, ...addressObj}; console.log(combinedObj); /* expected output: { "firstname": "John", "lastname": "Doe", "city": "some city", "state": "some state" } */
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