JavaScript_course

Variables

Variable is like a glass of water that you can put/take something into/from it and use it when you need it. So basically data can be stored in variables.

How to declare a variable?

Before you can use a variable, your need to announce that you want to use it. This involves creating the variable and giving it a name. In programming world they call it variable declaration.

variable

You can declare and assign value at the same time

assign

Rules for naming variables

  1. Variable name begin with a letter, dollar sign ($), or underscore (_). It must NOT begin with a number.
  2. The name can contain letters, numbers, dollar sign ($), or an underscore (_). Note that you must not use a dash(-) or a period (.) in a variable name.
  3. You cannot use keywords or reserved words. for example var.
  4. All variables are case sensitive. Case-Sensitive which mean that firstname is not equal to firstName.
  5. Use a name that describes the kind of information that the variable stores.
  6. If your variable name is made up of more than one word, use either camel-case or snake-case

Can you specify the valid variable names:

Variable name Is Valid
firstName Yes
Var# No
first_name Yes
num1 Yes
first name No
first-name No
1number No
$result Yes

Variable data types

JavaScript distinguishes between numbers strings, and true or false values known as Booleans, Functions, Arrays, Objects.

For now we will see only 3 major type which are strings,numbers,boolean.

let variableNumber = 0.75;
let variableString = "I love JS!";
let variableBool1 = true;
let variableBool2 = false;

Ahmed write them c02/js/numeric-variable Program

Ahmed write them c02/js/string-variable Program

Ahmed write them c02/js/string-with-quotes Program

Ahmed write them c02/js/boolean-variable Program

Ahmed write them c02/js/shorthand-variable Program

Ahmed write them c02/js/update-variable Program

Using quotes inside a string

Sometimes you will want to use a double or single quote mark within a string. and this will related to the internal string.

In ES6 there is a special string forming called the back tick which is used to set variables in between string without using + to concatenating stings

References and Terms:

:information_source: Read more about Camel case

:information_source: Read more about Snake case