It‘s common in Javascript for functions to accept different argument types and to also return different types. In this lesson we learn how to ‘teach‘ Typescript about these dynamic functions so that we can still benefit from the powerful static type analysis.
const getTasks = (taskname: string, x: any) : any => { if(typeof x === ‘function‘){ return {taskname, fn: x}; } if(Array.isArray(x)){ return {taskname, deps: x}; } }; const task1 = getTasks(‘taskname1‘, [‘dep1‘, ‘dep2‘]); const task2 = getTasks(‘taskname2‘, function(){}); task1.fn(); // Runtime Error, fn not exists on task1 task2.deps; // Runtime Error, deps not exists on task2
In the code above, the IDE cannot help much during the compile time.
But if we use Function overloads, then IDE can help to check error:
interface GroupTask { taskname:string deps:string[] } interface Task { taskname:string fn:Function } function getTasks(taskname:string, x:string[]):GroupTask function getTasks(taskname:string, x:Function):Task function getTasks(taskname:string, x:any):any { if (typeof x === ‘function‘) { return {taskname, fn: x}; } if (Array.isArray(x)) { return {taskname, deps: x}; } } const task1 = getTasks(‘taskname1‘, [‘dep1‘, ‘dep2‘]); const task2 = getTasks(‘taskname2‘, function () { }); task1.fn // Property ‘fn‘ doesn‘t not exist on type ‘GrouptTask‘ task2.deps // Property ‘deps‘ doesn‘t not exist on type ‘Task‘
[TypeScript] Function Overloads in Typescript
原文：http://www.cnblogs.com/Answer1215/p/5592632.html