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JavaScript Uses for Closures

Posted by Ewerton Luna
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Ewerton Luna
Full Stack JavaScript Techdegree Graduate 24,031 Points

I thought I get "let" until I saw this video. How does "let" solve this problem, exactly?

var buttons = document.getElementsByTagName('button');

for(var i = 0; i < buttons.length; i += 1) {
    var button = buttons[i];
    let buttonName = button.innerHTML;
    button.addEventListener('click', function(){
    console.log(buttonName);
  });
}

If the let keyword has a block scope, I think that, after the loop is finished, shouldn't exist a reference to the buttonName variable anymore, making the click event log "undefined".

Isn't that right? The variable declared with "let" only exists for that block, so I think that, after the for loop is done, the buttonName variable wouldn't be acessable anymore.

Can someone please explain how does this work in detail?

Thank you!

Brandon Khan
Brandon Khan
21,619 Points
Brandon Khan
Brandon Khan
21,619 Points

let allows for block scope as you are saying, each time your loop runs let will make a new variable not override the last one like with var. In your example buttonName is only accessible in the for loop. Also note i is accessible in function scope or global depending on the rest of your code. This may be an older video I'm not sure if closer in functions are needed after js got let and const.