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lib.d.ts: Include undefined in return type of JSON.stringify() #19097

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lib.d.ts: Include undefined in return type of JSON.stringify() #19097

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4 changes: 2 additions & 2 deletions src/lib/es5.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -955,14 +955,14 @@ interface JSON {
* @param replacer A function that transforms the results.
* @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
*/
stringify(value: any, replacer?: (key: string, value: any) => any, space?: string | number): string;
stringify(value: any, replacer?: (key: string, value: any) => any, space?: string | number): string | undefined;
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I do not think you want everyone to have to handle undefined when calling JSON.stringify, it is just cases where hte input is undefined or possibly a function. for these, i would add overloads..e.g

stringify(value: number | string | boolean | null | object, replacer?: (key: string, value: any) => any, space?: string | number): string;
stringify(value: any, replacer?: (key: string, value: any) => any, space?: string | number): string | undefined;

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also pinging @DanielRosenwasser and @RyanCavanaugh for feedback

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@MazeChaZer MazeChaZer Oct 11, 2017 •
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Yeah, narrowing down when undefined may appear would be great. I'm afraid this overload wouldn't catch function () {}, because it is of type object. Calling JSON.stringify(function () {}) would use the first provided overload, although the return value is undefined. Example on TypeScript Playground
Is it even possible to distinguish functions from “normal” objects in JavaScript? This is an area where I have very little knowledge.
Perhaps we can add one more overload before the other two that uses the Function type?

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sure.

/**
* Converts a JavaScript value to a JavaScript Object Notation (JSON) string.
* @param value A JavaScript value, usually an object or array, to be converted.
* @param replacer An array of strings and numbers that acts as a approved list for selecting the object properties that will be stringified.
* @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
*/
stringify(value: any, replacer?: (number | string)[] | null, space?: string | number): string;
stringify(value: any, replacer?: (number | string)[] | null, space?: string | number): string | undefined;
}

/**
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30 changes: 15 additions & 15 deletions tests/baselines/reference/json.stringify.types
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Expand Up @@ -4,50 +4,50 @@ var value = null;
>null : null

JSON.stringify(value, undefined, 2);
>JSON.stringify(value, undefined, 2) : string
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>JSON.stringify(value, undefined, 2) : string | undefined
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>JSON : JSON
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>value : null
>undefined : undefined
>2 : 2

JSON.stringify(value, null, 2);
>JSON.stringify(value, null, 2) : string
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>JSON.stringify(value, null, 2) : string | undefined
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>JSON : JSON
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>value : null
>null : null
>2 : 2

JSON.stringify(value, ["a", 1], 2);
>JSON.stringify(value, ["a", 1], 2) : string
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>JSON.stringify(value, ["a", 1], 2) : string | undefined
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>JSON : JSON
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>value : null
>["a", 1] : (string | number)[]
>"a" : "a"
>1 : 1
>2 : 2

JSON.stringify(value, (k) => undefined, 2);
>JSON.stringify(value, (k) => undefined, 2) : string
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>JSON.stringify(value, (k) => undefined, 2) : string | undefined
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>JSON : JSON
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>value : null
>(k) => undefined : (k: string) => undefined
>k : string
>undefined : undefined
>2 : 2

JSON.stringify(value, undefined, 2);
>JSON.stringify(value, undefined, 2) : string
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>JSON.stringify(value, undefined, 2) : string | undefined
>JSON.stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>JSON : JSON
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string; }
>stringify : { (value: any, replacer?: ((key: string, value: any) => any) | undefined, space?: string | number | undefined): string | undefined; (value: any, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string | undefined; }
>value : null
>undefined : undefined
>2 : 2
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