Error typeof type guards

[ghost]

export async function add(params: { [key: string]: string | string[] }): Promise<string> {
 if (!params.birthday || typeof params.birthday !== "string" || !Date.parse(params.birthday))
{
...
}
}

Get an Typscript Error on !Date.parse(params.birthday) because params.birthday can be a string or string []

Possible to make also object typeof recognize it as a type guard ?

[ghost]

Duplicate of #17567
This actually works in typescript@next thanks to #19838.

[ghost]

I try the [email protected] => Not solve the issue.
Not certain you get the issue.
I make a motion on : "Luckily, you don’t need to abstract typeof x === "number" into its own function because TypeScript will recognize it as a type guard on its own. That means we could just write these checks inline."
From : https://www.typescriptlang.org/docs/handbook/advanced-types.html
This recognize seems to work on primitive but not on object like in my example : typeof params.birthday !== "string"

[ghost]

Are you sure you installed it successfully? I don't see an error at Date.parse(params.birthday) when compiling with [email protected]. Could you check tsc -- version to make sure you're using the latest?

[ghost]

Yes : Version 2.7.0-dev.20171212
this is my example function :

export function test(params: ParsedUrlQuery): void {
    try {
        if (typeof params.birthday !== "string" || !Date.parse(params.birthday)) {
            throw (new AppError("Birthday invalid.", BAD_REQUEST));
        }
    } catch {
        console.log("So bad");
    }
}

and here my temporary patch:

export function test(params: ParsedUrlQuery): void {
    try {
        if (typeof params.birthday !== "string" || !Date.parse(params.birthday as string)) {
            throw (new AppError("Birthday invalid.", BAD_REQUEST));
        }
    } catch {
        console.log("So bad");
    }
}

and the : interface ParsedUrlQuery { [key: string]: string | string[]; }

[ghost]

I don't get a compile error in this example:

interface ParsedUrlQuery { [key: string]: string | string[]; }
function test(params: ParsedUrlQuery): boolean {
    return typeof params.birthday !== "string" || !Date.parse(params.birthday);
}

Do you? If you do, what tsconfig settings do you have?

[ghost]

{
  "compilerOptions": {
    /* Basic Options */
    "target": "es5",
    /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */
    "module": "commonjs",
    /* Specify module code generation: 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
    "lib": [
      "es2015"
    ],
    /* Specify library files to be included in the compilation:  */
    // "allowJs": true,                       /* Allow javascript files to be compiled. */
    // "checkJs": true,                       /* Report errors in .js files. */
    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
    "declaration": false,
    /* Generates corresponding '.d.ts' file. */
    "sourceMap": false,
    /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    "outDir": "./",
    /* Redirect output structure to the directory. */
    "rootDir": "./",
    /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    "removeComments": true,
    /* Do not emit comments to output. */
    // "noEmit": true,                        /* Do not emit outputs. */
    "importHelpers": true,
    /* Import emit helpers from 'tslib'. */
    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
    /* Strict Type-Checking Options */
    "strict": true,
    /* Enable all strict type-checking options. */
    "noImplicitAny": true,
    /* Raise error on expressions and declarations with an implied 'any' type. */
    "strictNullChecks": true,
    /* Enable strict null checks. */
    "noImplicitThis": true,
    /* Raise error on 'this' expressions with an implied 'any' type. */
    "alwaysStrict": true,
    /* Parse in strict mode and emit "use strict" for each source file. */
    /* Additional Checks */
    "noUnusedLocals": true,
    /* Report errors on unused locals. */
    "noUnusedParameters": true,
    /* Report errors on unused parameters. */
    "noImplicitReturns": true,
    /* Report error when not all code paths in function return a value. */
    "noFallthroughCasesInSwitch": true,
    /* Report errors for fallthrough cases in switch statement. */
    /* Module Resolution Options */
    "moduleResolution": "node",
    /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
    // "typeRoots": [],                       /* List of folders to include type definitions from. */
    // "types": [],                           /* Type declaration files to be included in compilation. */
    "allowSyntheticDefaultImports": true,
    /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
    /* Source Map Options */
    // "sourceRoot": "./",                    /* Specify the location where debugger should locate TypeScript files instead of source locations. */
    // "mapRoot": "./",                       /* Specify the location where debugger should locate map files instead of generated locations. */
    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
    /* Experimental Options */
    "experimentalDecorators": true,
    /* Enables experimental support for ES7 decorators. */
    "emitDecoratorMetadata": true /* Enables experimental support for emitting type metadata for decorators. */
  },
  "compileOnSave": false,
  "exclude": [
    "./node_modules"
  ]
}

[ghost]

Using that exact tsconfig.json, and a project with a single file containing the exact text from my above comment, I get no error when running tsc. My tsc --version is Version 2.7.0-dev.20171212.

[ghost]

Ok thanks. I will investigate. Maybe conflict with my TSlint.

[ghost]

Ok confirm the Version 2.7.0-dev.20171212 solved the issue. I had a conflict between global and local package in the last test. Thanks for your job!
For information the exact compile error in the 2.6.2 was : error TS2345: Argument of type 'string | string[]' is not assignable to parameter of type 'string'.
Type 'string[]' is not assignable to type 'string'.