Javascript Block Scope, Falsy Value, Error Handling

Let's see javascript block scope( {...}), False values and throw, Error Handling statements. Learning test is written using Jasmine. Please refer Jasmine usage which I wrote before if you have interest it.

1. Javascript don't have Block Scope before ECMAScript6

	it("donot have a block scope prior to ECMAScript6", function() {
	var x = 1;
	{
	var x = 2;
	}
	expect(x).toBe(2);
	});

view raw js-learning-blockscope.js hosted with ❤ by GitHub

2. Falsy value

false, undefined, 0, empty string(""), NaN are treated as a false.

	it("Falsy value", function() {
	var falsyAray = [false, undefined, 0, '', NaN];
	for (x of falsyAray) {
	expect((x? true:false)).toBe(false);
	}
	});

view raw js-learning-falsyvalue.js hosted with ❤ by GitHub

3. Throw expression, try - catch - finally

Javascript can throw any expression using "throw" keyword. The throwed expression can be used in catch statement like [line 15], [line 43]. You can see how to use try - catch -finally statements.

	it("you may throw any expression, try - catch- finally", function() {
	var throwFunc = function() {
	throw "error";
	}
	expect(throwFunc).toThrow();
	throwFunc = function() {
	throw 42;
	}
	expect(throwFunc).toThrow();
	try {
	throwFunc();
	} catch (e) {
	expect(e).toBe(42);
	}
	throwFunc = function() {
	throw function() {
	return "hello";
	};
	}
	expect(throwFunc).toThrow();
	function MyException (m) {
	this.message = m;
	};
	MyException.prototype.toString = function () {
	return this.m;
	};
	throwFunc = function() {
	throw new MyException("Oops!");
	};
	expect(throwFunc).toThrow();
	try {
	throwFunc();
	} catch (e) {
	expect(e.message).toBe("Oops!");
	}
	var i = 0;
	try {
	i++;
	expect(i).toBe(1);
	throwFunc();
	} catch (e) {
	i++;
	expect(e.message).toBe("Oops!");
	expect(i).toBe(2);
	} finally {
	i++;
	expect(i).toBe(3);
	}
	});

view raw js-learning-throwtrycatchfinally.js hosted with ❤ by GitHub

4. Error Object

You can throw Error Object easily.

	it("thorw Error", function() {
	var throwErrorFunc = function() {
	throw (new Error("Oops!"));
	}
	expect(throwErrorFunc).toThrow();
	expect(throwErrorFunc).toThrowError("Oops!");
	expect(throwErrorFunc).toThrowError(Error);
	expect(throwErrorFunc).toThrowError(Error, "Oops!");
	});

view raw js-learning-throwError.js hosted with ❤ by GitHub

5. Reference

- MDN - https://developer.mozilla.org/en/docs/Web/JavaScript
- Jasmine - http://jasmine.github.io/2.3/introduction.html