typescript 之 literal type

字面量类型

typescript
let str = `123`;
str = `456`;

const _constStr = `hello`;
// _constStr = `` //常量赋值错误

let x: `hello` = `hello`;

function logText(str: string, alignItems: 'left' | 'center' | 'right') {}

logText('hello', 'left');

function compare(a: string, b: string): -1 | 0 | 1 {
  return a === b ? 0 : a > b ? 1 : -1;
}

interface Options {
  width: number;
}

function setWidth(x: Options | 'auto') {}

setWidth({
  width: 100,
});

setWidth('auto');

let b1: false = false;
let b2: true = true;

const obj = {
  count: 0,
};

if (true) {
  obj.count = 1;
}

function req(url: string, method: 'GET' | 'POST' | 'PUT') {}

const opt = {
  url: 'https://api.user',
  method: 'GET',
};

req(opt.url, opt.method /*as 'GET'*/); // 类型“string”的参数不能赋给类型“'GET'|'POST'|'PUT'”的参数。