Basic JavaScript - Global Scope and Functions

JavaScript
1

Tell us what’s happening:
Describe your issue in detail here.
Why you don’t have to put let,var or const before oopsGlobal? it is not declared anywhere.
Your code so far

// Declare the myGlobal variable below this line
let myGlobal=10;

function fun1() {
  // Assign 5 to oopsGlobal here
   oopsGlobal=5;
}

// Only change code above this line

function fun2() {
  let output = "";
  if (typeof myGlobal != "undefined") {
    output += "myGlobal: " + myGlobal;
  }
  if (typeof oopsGlobal != "undefined") {
    output += " oopsGlobal: " + oopsGlobal;
  }
  console.log(output);
}

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/112.0.0.0 Safari/537.36

Challenge: Basic JavaScript - Global Scope and Functions

Link to the challenge:

2

Hi, so in this scenario, the oopsGlobal becomes a new variable that you are declaring within the block. As it is a block scope variable, it is new and would not be found elsewhere in the code - specific to this function only. I hope this helps :slight_smile:

3

so if i declare it in the function,i dont have to put let or const?i dont understand your explanation.

4

You should use let or const. This challenge is showing why it’s bad to not declare your variables.

5

When you do not declare a variable JS tries to be “helpful” by placing it on the global object. Which is just a huge foot gun and not actually helpful.

Open a new browser tab, open the console Shift + Ctrl + J paste the code below.

function createGlobalVariable() {
  oopsGlobal = 5;
}

createGlobalVariable();
console.log(globalThis.oopsGlobal); // 5

Do the same again in strict mode and it will fail (remember to open a new tab).

'use strict'
function createGlobalVariable() {
  oopsGlobal = 5;
}

createGlobalVariable();
console.log(globalThis.oopsGlobal); // Uncaught ReferenceError: oopsGlobal is not defined

Links:

6

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