export class Thread {
id: string;
lastMessage: Message;
name: string;
avatarSrc: string;
constructor(id?: string,
name?: string,
avatarSrc?: string) {
this.id = id || uuid();
this.name = name;
this.avatarSrc = avatarSrc;
}
}
在id吗?这是什么?用的?
当前回答
的吗?在参数中表示一个可选参数。Typescript编译器不需要填写此参数。查看下面的代码示例了解更多细节:
// baz: number | undefined means: the second argument baz can be a number or undefined
// = undefined, is default parameter syntax,
// if the parameter is not filled in it will default to undefined
// Although default JS behaviour is to set every non filled in argument to undefined
// we need this default argument so that the typescript compiler
// doesn't require the second argument to be filled in
function fn1 (bar: string, baz: number | undefined = undefined) {
// do stuff
}
// All the above code can be simplified using the ? operator after the parameter
// In other words fn1 and fn2 are equivalent in behaviour
function fn2 (bar: string, baz?: number) {
// do stuff
}
fn2('foo', 3); // works
fn2('foo'); // works
fn2();
// Compile time error: Expected 1-2 arguments, but got 0
// An argument for 'bar' was not provided.
fn1('foo', 3); // works
fn1('foo'); // works
fn1();
// Compile time error: Expected 1-2 arguments, but got 0
// An argument for 'bar' was not provided.
其他回答
它将参数标记为可选。
TypeScript手册https://www.typescriptlang.org/docs/handbook/2/functions.html#optional-parameters TypeScript Deep Dive https://basarat.gitbook.io/typescript/type-system/functions#optional-parameters
参数?: type是参数:type | undefined的简写
那么有什么不同呢?问号表示“可选”。更精确的参数?参数:type | undefined = undefined
从TypeScript 4.7开始，编译器是这样处理这些场景的:
interface OptTest {
test: string
test2: string
test3?: string
test4?: string | null
test5: string | null
test6: null
}
const testVar: OptTest = {}
// Type '{}' is missing the following
// properties from type 'OptTest': test, test2, test5, test6
这将使变量的类型为Optional。否则声明的变量显示“未定义”，如果这个变量没有被使用。
export interface ISearchResult {
title: string;
listTitle:string;
entityName?: string,
lookupName?:string,
lookupId?:string
}
的吗?在参数中表示一个可选参数。Typescript编译器不需要填写此参数。查看下面的代码示例了解更多细节:
// baz: number | undefined means: the second argument baz can be a number or undefined
// = undefined, is default parameter syntax,
// if the parameter is not filled in it will default to undefined
// Although default JS behaviour is to set every non filled in argument to undefined
// we need this default argument so that the typescript compiler
// doesn't require the second argument to be filled in
function fn1 (bar: string, baz: number | undefined = undefined) {
// do stuff
}
// All the above code can be simplified using the ? operator after the parameter
// In other words fn1 and fn2 are equivalent in behaviour
function fn2 (bar: string, baz?: number) {
// do stuff
}
fn2('foo', 3); // works
fn2('foo'); // works
fn2();
// Compile time error: Expected 1-2 arguments, but got 0
// An argument for 'bar' was not provided.
fn1('foo', 3); // works
fn1('foo'); // works
fn1();
// Compile time error: Expected 1-2 arguments, but got 0
// An argument for 'bar' was not provided.
