Javascript Expression and Operators

Let's see Javascript expression and operator. You can learn the basic content from MDN's  Expressions and Operators . We'll see Javascript specific things and something is good to know. Learning test is written using Jasmine. Please refer Jasmine usage which I wrote before if you have interest it. 

1. equal, strict equal
If the type is different like [line5], Javascript try to converting type automatically since javascript is dynamic typing language. If you want to check equality with the actual type, you can use strict equal operator like [line 7].

	it("equals, strict equal", function() {
	var num1 = 1;
	expect(num1 == 1).toBe(true);
	expect(num1 == "1").toBe(true);
	expect(num1 === 1).toBe(true);
	expect(num1 === "1").toBe(false);
	var str1 = "1";
	expect(str1 != 1).toBe(false);
	expect(str1 != "1").toBe(false);
	expect(str1 !== 1).toBe(true);
	expect(str1 !== "1").toBe(false);
	});

view raw js-learning-operator-equals.js hosted with ❤ by GitHub

2. negation, plus
The plus(+) operator convert to number.

	it("negation, plus operator", function() {
	var num1 = 1;
	expect(-num1).toBe(-1);
	var str1 = "1";
	expect(+str1).toBe(1);
	});

view raw js-learning-operator-negationplus.js hosted with ❤ by GitHub

3. string operator

	it("string opertor", function() {
	var str1 = "hi";
	expect(str1 + " hello").toBe("hi hello");
	});

view raw js-learning-operator-string.js hosted with ❤ by GitHub

4. delete operator
The "delete" operator delete specific property of object or specific index of array. The deleted object would be undefined like [line 9, line 15].

	it("delete operator", function() {
	var phone = {
	"number" : "123-45678",
	"owner" : "thinkhard.j.park"
	}
	expect(phone.owner).toBe("thinkhard.j.park");
	delete phone.owner;
	expect(phone.owner).toBe(undefined);
	var aray = [0,1,2,3,4];
	expect(aray[0]).toBe(0);
	delete aray[0];
	expect(aray[0]).toBe(undefined);
	expect(0 in aray).toBe(false);
	})

view raw js-learning-operator-delete.js hosted with ❤ by GitHub

5. typeof
You can know the type using "typeof" operator.

	it("typeof", function() {
	var myFun = new Function("5 + 2");
	var shape = "round";
	var size = 1;
	var today = new Date();
	expect(typeof myFun).toBe("function");
	expect(typeof shape).toBe("string");
	expect(typeof size).toBe("number");
	expect(typeof today).toBe("object");
	expect(typeof notdefined).toBe("undefined");
	expect(typeof null).toBe("object");
	expect(typeof undefined).toBe("undefined");
	});

view raw js-learning-operator-typeof.js hosted with ❤ by GitHub

6. void(expression)
The "void" operator evaluates expression like [line 5]. But don't return anything like [line6].

	it("void(expression) : void evaluate expression but not return.", function() {
	var myFun = function(a, b) {return a + b};
	var result = 0;
	expect(void(result = myFun(2, 5))).toBe(undefined);
	expect(result).toBe(7);
	});

view raw js-learning-operator-void.js hosted with ❤ by GitHub

7. in operator
The "in" operator check whether specific element is contained in Object or Array.

	it("in operator return true if the specified property is in the specified object", function() {
	var trees = ["redwood", "bay", "cedar", "oak", "maple"];
	expect(0 in trees).toBe(true);
	expect(5 in trees).toBe(false);
	//should use index number
	expect("bay" in trees).toBe(false);
	expect("PI" in Math).toBe(true);
	var myString = new String("coral");
	expect("length" in myString).toBe(true);
	var mycar = { make: "Honda", model: "Accord", year: 1998 };
	expect("make" in mycar).toBe(true);
	});

view raw js-learning-operator-in.js hosted with ❤ by GitHub

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