Like any programming language, variables in JavaScript store values.
Use the let keyword to create a JavaScript variable.
let studentName = “John”;
console.log(studentName);
Type the above piece of code in Plunker editor https://plnkr.co/edit/?p=preview. Press F12 IN Chrome to see the output in console.
Its a good practice to create variables in JS using camel case notation.
Use comma to create multiple variables.
let studentName = “John”,
studentId = “111”;
console.log(studentName, studentId);
If you are using apostrophe, then use \ ( back slash for it to show)
let yourName = ‘What\’s your name?’;
console.log(yourName);
Numeric Variables in JavaScript
let price = 5.00;
console.log(price);
The output is : 5
Arithmetic operators for numeric variables
JavaScript uses the common arithmetic numeric variables.
+ for addition , – for subtraction , * for multiplication, / for division,% for modulus.
Adding Numeric variable with String
If you try to add a numeric variable with a string, it treats the number as a string.
let myId = 1,
myName = “Amit”;
console.log(myId + myName);
The output is: 1Amit
Some Interesting behavior of JS with numbers
let abc = 2.1 + 2.3;
console.log(abc);
The output is: 4.399999999999999
let abc = 2 / 0;
console.log(abc);
The output is: Infinity
let abc = -2 / 0;
console.log(abc);
The output is: -Infinity
let abc = 0/ 0;
console.log(abc);
The output is: NaN
You can use the typeof Keyword to know the type of a variable
let abc = 0/ 0;
console.log(typeof(abc));
The output is: Number
JavaScript Boolean variables
Boolean can value as ‘true’ or ‘false’.
let abc = true;
console.log(typeof(abc));
The output is: boolean
Undefined and Null in JavaScript
undefined : JavaScript will initialize variables to undefined
null: developers cannot initialize a variable to undefined. They should assign a variable to null.
let abc;
console.log(abc);
The output is: undefined
let abc;
abc = null;
console.log(abc);
The output is: null
efined
let abc;
abc = null;
console.log(abc, typeof(abc));
The output is: null “object”
Concatenate Strings in JavaScript
let firstName = “John”,
lastName = “Doe”;
console.log(firstName + lastName);
The output is: JohnDoe