Declare a variable:let x: number; Do some complicated logic to possibly assign it If it wasn't assigned, provide a default value. Currently, we can't compile this function. We get an error for!xsayingVariable 'x' is used before being assigned. ...
I'm also gettingVariable ... is used before being assignedeven though it is assigned. Simple repro: // strict: true in tsconfigfunctionfoo(a:1|2|3){if(a==1){return"a";}letx:string;if(a==2){x="b";}elseif(a==3){x="c";}else{console.log(a);// a has type 'never'}retu...
问带有async和await的Typescript :变量在为assigned.ts之前使用(2454)ENJavaScript ES7中的 async/await ...
1188 错误 Only a single variable declaration is allowed in a 'for...of' statement. "for...of" 语句中只允许单个变量声明。 1189 错误 The variable declaration of a 'for...in' statement cannot have an initializer. "for...in" 语句的变量声明不能有初始化表达式。 1190 错误 The variable decla...
// Variable 'x' is used before being assigned.(2454) console.log(2 * x); // Error function initialize() { x = 10; } 1. 2. 3. 4. 5. 6. 7. 很明显该异常信息是说变量 x 在赋值前被使⽤了,要解决该问题,我们可以使⽤确定赋值断⾔: ...
// 例子 3leta:numberconsole.log(a)// Error - Variable 'n' is used before being assigned.letb!:numberconsole.log(b)// OK - `!` 表示,你会给 b 一个赋值,不用编译器关心 可选链?. ?.遇到null或undefined就可以立即停止某些表达式的运行,并返回undefined ...
Significance of using a variable before assigning a value, Value has already been assigned to a previously used variable, TypeScript Error: Usage of Variable with Two Possible Types Before Assignment, Unassigned Value Causes Data Filtering Failure
console.log(name); // Error: [ts] Variable 'address' is used before being assigned. 对于可能是undefined的变量: 使用显式声明 提示编译错误:当使用一个可能为null的变量的时候。 使用前,需要确定不是undefined. 代码语言:javascript 代码运行次数:0 运行 AI代码解释 var address: string | undefined; /...
accountType ="user";// 报错:roperty 'email' has no initializer and is not definitely assigned in the constructor.// 属性“email”没有初始化表达式,且未在构造函数中明确赋值。email:string;address:string|undefined;constructor(name:string) {this.name= name;// Note that this.email is not set} ...
// Error! Variable 'x' is used before being assigned. function initialize() { x = 10; } 添加!修饰:let x!: number,则可以修复这个问题 我们也可以在表达式中使用!,类似variable as string和<string>variable: let x: number; initialize(); ...