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JavaScript JavaScript Loops, Arrays and Objects Simplify Repetitive Tasks with Loops For Loops

why use += for adding html?

I tried this code replacing += with + (which is what i thought it would be!) and it did not run. Can someone explain why += is used here?

var html = ' ';

for(var i = 1; i <= 10; i +=1) {
  html += '<div>' + i + '</div>';

Thank you

1 Answer

David Diehr
David Diehr
16,457 Points

(First off, I'm a beginner too so I may be wrong) I would say that it wouldn't run, because without an "=" then what is that line of code doing? You're just adding a variable to a string to a div. But you're not saying what to do with those added values. The "=" is telling the program to use those added (concatenated, actually) values to set a new value for the html variable. The code uses "+=" in order to add the new values to the existing html value. Which is why the html value that is written in the end includes all the divs.

William Li
William Li
Courses Plus Student 26,867 Points

David, this is a great answer.

Let me add that, for beginner, the syntax of this code i +=1 may look kinda strange. But in the nutshell.

i += 1

// is same as
i = i + 1

You ask the computer to compute i + 1, and assign the result back to i. This is how you increment the value of i by 1. And since when writing JavaScript, it's so common to increment a variable by 1, the language gives you a shorthand way of writing it i += 1.