consta=document.getElementById("a") 对我自己来说,使用 TS 之前,我忽略了document.getElementById的返回值还可能是 null,这种不经意的忽略也许在未来就会造成一个意想不到的 bug。 使用TS,在编辑器中就会明确的提醒我们 a 的值可能为 null。 我们并不一定要处理值 null 的情况,使用 const a = document.g...
TypeScriptPlayground-正常 有趣的是，有一个名为preserveConstEnums的tsconfig选项，它也能完成这个任务;...
Down: 1, Left: 2, Right: 3, } as const; EDirection.Up; (enum member) EDirection.Up = 0 ODirection.Up; (property) Up: 0 // Using the enum as a parameter function walk(dir: EDirection) {} // It requires an extra line to pull out the values type Direction = typeof ODirection...
By doing this, we get an object that is read-only and protected. Note that the read-only definition is only shown when we hover the mouse over the directionEnum const: const directionEnum: Readonly<{ UP: string; DOWN: string; }> The Object.freeze method prevents the modification of ex...
{ name:'Tom', animal:'cat'}, { name:'Jerry', animal:'mouse'}, ];// 只能包含对象 letarr:any[] = ['hello',1,true];// 啥都行,回到了 JS ids.push(6); ids.push('7');// ERROR: Argument of type 'string' is not assignable to parameter of ...
name: string; } interface IState { count: number; } class App extends React.Component<IProps,IState>{ state = { count: 0 }; render() { return ( <div> {this.state.count} {this.props.name} </div> ); } } export default App; ...
const user = new User(); user.firstName = "Timber"; user.lastName = "Saw"; user.age = 25; await user.save(); 其次看一下 Data Mapper 型的写法: // 模型定义 import {Entity, PrimaryGeneratedColumn, Column} from "typeorm"; @Entity() export class User { @PrimaryGeneratedColumn() id:...
to enum gets key by string value in typescript by using object.key, object.value and indexOF() This is how we can enum gets by string value in typescript by using the object.key, object. value and indexOf(). Check out:How to get string between 2 characters in Typescript ...
TypeScriptPlayground-正常 有趣的是，有一个名为preserveConstEnums的tsconfig选项，它也能完成这个任务;...
The entire collection is then used during each of the stages.This is in contrast to how Babel processes files - where Babel does file in file out, TypeScript does project in, project out. This is why enums don't work when parsing TypeScript with Babel for example, it just doesn't ...