Variables in JavaScript: Declaration, Initialization, and Scope

A JavaScript variable is simply a name of storage location. There are two types of variables in JavaScript : local variable and global variable. 

There are some rules while declaring a JavaScript variable (also known as identifiers).

• Variables are the identifiers to store data values in our code.
• var is the keyword to declare a variable.
• ‘=’ is the operator to assign a value to a variable.
• A variable must start with _ or $ or letter. 99temp is invalid whereas _99temp is valid.
• In ES2015(known as ECMAscript), two other ways to declare variables were introduced- let and const. We can use these 2 keywords to define variables(now recommended).

Correct JavaScript variables

<span class="pln">
</span><span class="kwd">var</span><span class="pln"> x </span><span class="pun">=</span><span class="pln"> </span><span class="lit">10</span><span class="pun">;</span><span class="pln">  
</span><span class="kwd">var</span><span class="pln"> _value</span><span class="pun">=</span><span class="str">"hello"</span><span class="pun">;</span><span class="pln">  
</span>

Incorrect JavaScript variables

<span class="pln">
</span><span class="kwd">var</span><span class="pln">  </span><span class="lit">123</span><span class="pun">=</span><span class="lit">310</span><span class="pun">;</span><span class="pln">  
</span><span class="kwd">var</span><span class="pln"> </span><span class="pun">*</span><span class="pln">bb</span><span class="pun">=</span><span class="lit">340</span><span class="pun">;</span><span class="pln">  
</span>

In later chapter we will discuss about local and global variable.

Solve these below questions.

Sample Question 1: