Option Explicit

Option Explicit: Why we need this statement while writing VBScript?

-- By default, VBScript will allow use of variables without declaration which leads to lot of mis-spell, type and wrong variable name errors.
-- This will force the VBScript Engine not to accept the variables without declaration before its first use.
-- Normally, Used to avoid typo errors, giving wrong variable names, redefining variables by mistake, etc.

Consider the below script:

1. Dim var1
2. var1 = 10
4. 'This line will not throw any error like "Variable undefined"
5. var2 = 20
7. 'This line will not throw any error like "Variable redefined"
8. Dim var1

After inserting Option Explicit Statement, it will throw error.

1. Option Explicit
2. Dim var1
3. var1 = 10
4. var2 = 20     'This line will throw error "Variable undefined"

Also,

1. Option Explicit
2. Dim var1
3. var1 = 10
5. Dim var1      'This line will throw error "Variable redefined"

The same functionality is available in JavaScript by typing "use strict" like below;

1. "use strict";
2. var var1 = 10;
3. alert(var1);