TypeAssert

Simple run-time type checker for JS. Ensures that function arguments match a specified type signature.

How can I use it?

Include the typeAssert.js file into your project via HTML <script> tag or AMD/CommonJS require(). Specify the allowed argument types on the the first line of any function:

function congrats(name, age){
	typeAssert(arguments, [String, Number]);
	return "Congratulations, " + name + "! You are " + age + " years old."; 
}
congrats("John", 27);

The agruments will be checked any time the function is invoked. A TypeError will be thrown, if any of the arguments does not match the specified type.

congrats("John", "Nineteen");
// Uncaught TypeError: TypeAssert failed for argument 2

How are types defined?

Constructor functions form the basic building blocks of type definitions. Under the hood TypeAssert makes an instanceof check against the constructor. Primitive types number, boolean and string are represented with the corresponding constructors Number, Boolean and String.

function Car(make){
	this.make = make;
}

function congrats(name, car){
	typeAssert(arguments, [String, Car]);
	return "Congratulations, " + name + " on your new " + car.make; 
}
congrats("John", new Car("Toyota") );

How can I define the type of array elements?

Use the array literal [ ] with a constructor function inside to define an array of certain type.

function congrats(name, cars){
	typeAssert(arguments, [String, [Car]]);
	return "Congratulations, " + name + ". You have " + cars.length + " cars"; 
}
congrats("John", [new Car("Toyota"), new Car("BMW")] );

How about more complex types?

Object interfaces can be defined with JS object literals describing the required properties & methods.

function congrats(data){
	typeAssert(arguments, [{toString: Function, location: {latitude: Number, longitude: Number}}]);
	return "Your location is " + data.toString(); 
}
congrats({
    toString: function(){
        return "(lat: " + this.location.latitude + ", lng: " + this.location.longitude + ")";
    }, 
    location: {latitude: 60.34, longitude: 24.45}
});

Why should I use TypeAssert?