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Fixed: TypeScript compile error#11

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gucong3000 wants to merge 1 commit into from
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Fixed: TypeScript compile error #11

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11 changes: 2 additions & 9 deletions index.d.ts
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Original file line numberDiff line numberDiff line change
Expand Up@@ -7,17 +7,10 @@ declare namespace PluginError {

/**
* @param plugin Plugin name
* @param message Error message
* @param error Base error / Error message
* @param options Error options
*/
new (plugin: string, message: string, options?: Options): PluginError;

/**
* @param plugin Plugin name
* @param error Base error
* @param options Error options
*/
new <E extends Error>(plugin: string, error: E, options?: Options): PluginError<E>;
new <E extends Error>(plugin: string, error: E | string, options?: Options): PluginError<E>;

/**
* @param plugin Plugin name
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41 changes: 41 additions & 0 deletions test/types/test.ts
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Original file line numberDiff line numberDiff line change
Expand Up@@ -51,3 +51,44 @@ import PluginError = require("plugin-error");
}
}

{
const PLUGIN_NAME = 'test';
function createPluginError(err: Error | string) {
return new PluginError(PLUGIN_NAME, err);
}
}

{
const PLUGIN_NAME = 'test';

interface IFooError extends Error {
foo: number;
}

function createPluginError(err: IFooError | string) {
return new PluginError(PLUGIN_NAME, err);
}

const fooError: IFooError = Object.assign(new Error('something broke'), {foo: 1});
const pluginError = createPluginError(fooError);
const foo: number = pluginError.foo;

@demurgosdemurgosJan 23, 2018•
edited
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Thanks again for the change and sorry for the back-and-forth.
At this point, foo should be number | undefined: if you invoke createPluginError("message"), then foo won't be defined. This was the reason why in my first message I said that an additional signature was required.

I then got confused in my reply two hours ago when I told you to merge the signatures: I should have stuck with my initial reply consisting in just updating the return type of your initial commit.

exportinterfaceConstructor{/** * @param options Options with plugin name and message */new(options: Options&{plugin: string,message: string}): PluginError;/** * @param plugin Plugin name * @param message Error message * @param options Error options */new(plugin: string,message: string,options?: Options): PluginError;/** * @param plugin Plugin name * @param error Base error * @param options Error options */new<EextendsError>(plugin: string,error: E,options?: Options): PluginError<E>;/** * @param plugin Plugin name * @param error Base error or error message * @param options Error options */new<EextendsError=Error>(plugin: string,error: E|string,options?: Options): PluginError<E|{[KinkeyofE]: undefined}>;/** * @param plugin Plugin name * @param options Options with message */new(plugin: string,options: Options&{message: string}): PluginError;}

Here is the explanation:

// Nitpick: The convention in TS is to avoid the `I` prefix for interfaces.interfaceFooErrorextendsError{foo: number;}functioncreateError1(error: FooError){constpluginError=newPluginError(PLUGIN_NAME,error);// In this case, we know that the second parameter is an error with a custom property `foo`// So the result will also have a property `foo`constfoo: number=pluginError.foo;}functioncreateError2(error: string){constpluginError=newPluginError(PLUGIN_NAME,error);// In this case, we know that the second parameter is a string. It means that the result is a simple `PluginError`// and does not have `foo`. The following code would cause a compilation error:// const foo: any = pluginError.foo;}functioncreateError3(error: FooError|string){constpluginError=newPluginError(PLUGIN_NAME,error);// In this case we don't know if we received an error instance or string: we cannot use the type-checker// to prove that `foo` is defined. The correct type for the `foo` property is `number | undefined`.constfoo: number|undefined=pluginError.foo;// It will be defined if we call `createError3(Object.assign(new Error("msg"), {foo: 1}));`// It will be undefined if we call `createError3("msg");`}

The FooBar case is not yet properly supported by the engine so it's better to not test it. Here is a better illustration of the problem:

interfaceNamed{name: string;foo: undefined;bar: undefined}interfaceNamedFooBar{name: string;foo: number;bar: number;}typeUnion=Named|NamedFooBar;functionexec(union: Union){if(union.foo!==undefined){// This fails with TS2322 when `strictNullChecks` is enabled.constbar: number=union.bar;}}

}

{
// Inference with union type on second parameter and dependent properties
const PLUGIN_NAME = 'test';

interface IFooBarError extends Error {
foo: number;
bar: number;
}

function createPluginError(err: IFooBarError | string) {
return new PluginError(PLUGIN_NAME, err);
}

const fooError: IFooBarError = Object.assign(new Error('something broke'), {foo: 1, bar: 2});
const pluginError = createPluginError(fooError);
const foo: number = pluginError.foo;
const bar: number = pluginError.bar;
}