Final answer:
The main difference between 'let' and 'var' in JavaScript is the scoping rules. 'var' is function or globally scoped and is hoisted, allowing it to be used before it's declared. In contrast, 'let' is block-scoped and not initialized until declared, resulting in a ReferenceError when accessed too early.
Step-by-step explanation:
Difference Between let and var in JavaScript
When it comes to declaring variables in JavaScript, let and var can seem similar but have distinct differences. The var keyword declares a variable globally or locally to an entire function irrespective of block scope. Variables declared with var are also hoisted, allowing them to be used in the code before they are actually declared.
On the other hand, let allows you to declare variables that are limited in scope to the block, statement, or expression in which they are used. This is known as block scoping. Unlike var, variables declared with let are not initialized until their definition is evaluated. Attempting to use a let variable before its declaration results in a ReferenceError. This behavior is known as the Temporal Dead Zone (TDZ).
The block scoping of let makes it a better choice for controlling the variable access in complex code, while var can lead to confusion when used in blocks such as for loops and if statements. Choosing between let and var often depends on the need for block level scoping and the use case in hand.