Question

im trying to insert a new div into the DOM with an id of “app”

var new_div = document.createElement("div");
var app_div = document.getElementById("app");
document.body.insertBefore(new_div, app_div);​

this gives me an error in the console:

Uncaught TypeError: Cannot call method ‘insertBefore’ of null

but i don’t know why?

Answer 1

You need to wrap your code to window.onload handler:

window.onload = function() {
    var new_div = document.createElement("div");
    var app_div = document.getElementById("app");
    document.body.insertBefore(new_div, app_div);
}

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Example on jsFiddle.