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let Variables

In the previous challenge, we created a variable called greeting. But it didn't look quite like what we've been practicing in the REPL.

let greeting = "Hello, World!";

Let's break it down:

  • let is a keyword that tells the JavaScript engine that we're creating a variable.
  • greeting is the variable's name. We may choose any valid name we like.
  • = is the assignment operator. It assigns the value to its right to the variable on its left. As we've seen, that could be a simple value or the result of a calculation.
  • "Hello, World!" is the value we're assigning to the variable.

But why did we use let? Why not just write:

greeting = "Hello, World!"

Let's find out. Click the ▶ button...

Whoops. JavaScript requires us to declare a variable before we can use it or assign a value to it. let is one way (but, we'll see, not the only way) to declare a variable. The REPL let us be a little sloppy. But in a script, we must declare our variables with a variable declaration keyword like let.

Let's fix the code by adding the let keyword:

let greeting = "Hello, World!";

Now click the ▶ button again. Better, right?

The takeaway: when creating a variable, you must declare it let or another variable declaration keyword.

Got it? Click the ✓ button to move on.