declare var foo:number;declare function greet(greeting: string): void;declare namespace myLib {function makeGreeting(s: string): string;let numberOfGreeting: number;}declare function getWidget(n: number): Widget;declare function getWidget(s: string): Widget[];declare class Greeter {constructor(g...
NAME= "Haha";//Uncaught TypeError: Assignment to constant variableconst obj ={ name:"TypeScript"}; obj.name= "Haha"; interface Info { readonly name: string; } const info: Info={ name:"TypeScript"}; info["name"] = "Haha";//Cannot assign to 'name' because it is a read-only pro...
但是你会发现在 src/styles/index.scss 全局样式文件中没有办法使用变量 . 因此需要给项目中引入全局变量 . 在style/variable.scss创建一个variable.scss文件! 在vite.config.ts文件配置如下: exportdefaultdefineConfig((config) =>{ css: { preprocessorOptions: { scss: { javascriptEnabled:true, additionalData:...
: string; } // 非空断言操作符 function nonNull(e?: Entity) { const s = e!.name; // 发生断言,抛出TypeError } try { nonNull(obj); } catch (e) { console.error("nonNull catch", e); // TypeError: Cannot read property 'name' of null } // 可选链 function optionalChaining(e?: E...
The other type of assertion signature doesn’t check for a condition, but instead tells TypeScript that a specific variable or property has a different type. 代码语言:javascript 代码运行次数:0 运行 AI代码解释 function assertIsString(val: any): asserts val is string { if (typeof val !== ...
functionlogProperty(target:any,key:string){deletetarget[key];constbackingField="_"+key;Object.defineProperty(target,backingField,{writable:true,enumerable:true,configurable:true});// property getterconstgetter=function(this:any){constcurrVal=this[backingField];console.log(`Get:${key}=>${currVal}`);...
? Diagnostics.Cannot_redeclare_block_scoped_variable_0 : Diagnostics.Duplicate_identifier_0; forEach(source.declarations, node => { error(getNameOfDeclaration(node) || node, message, symbolToString(source)); }); forEach(target.declarations, node => { ...
TypeScript can usually figure out a more specific type for a variable based on checks that you might perform. This process is called narrowing. Copy functionuppercaseStrings(x:string| number) {if(typeofx==="string") {// TypeScript knows 'x' is a 'string' here.returnx.toUpperCase(); ...
{includeInlayParameterNameHints:'none'|'literals'|'all';includeInlayParameterNameHintsWhenArgumentMatchesName:boolean;includeInlayFunctionParameterTypeHints:boolean;includeInlayVariableTypeHints:boolean;includeInlayVariableTypeHintsWhenTypeMatchesName:boolean;includeInlayPropertyDeclarationTypeHints:boolean;includeInlay...
typeof undeclaredVariable === 'undefined'; typeof null === 'object'; typeof false === 'boolean'; typeof Boolean(1) === 'boolean'; // Boolean() 会基于参数是真值还是虚值进行转换 // Symbols typeof Symbol() === 'symbol'; typeof Symbol('foo') === 'symbol'; ...