How can I get the URL for an API if the URL I want is in the API's JSON?

This is reapplying the click with every call:

function getAPI(apiurl){    $.getJSON(apiurl, function(data) {        //Does some stuff then        $(".nextPage").on("click", function(){            titleList.length = 0;            artistList.length = 0;            imgList.length = 0;            idList.length = 0;            $(".trackList").empty();            getAPI(data.next_href);        })      });}

Each time it's called, the number of click handlers goes up by 1 and each will be called.

To stop reapplying it, remove it then apply it. off() does the removal.

function getAPI(apiurl){    $.getJSON(apiurl, function(data) {        //Does some stuff then        $(".nextPage").off("click").on("click", function(){            titleList.length = 0;            artistList.length = 0;            imgList.length = 0;            idList.length = 0;            $(".trackList").empty();            getAPI(data.next_href);        })      });}

To make life easier in the future, separate your onclick binding from the getAPI call.

If the button isn't present in the DOM until some event happens, bind to a parent element and they'll be no need for off/on:

$("PARENT OF THE .nextPage BUTTON").on("click", ".nextPage", function(){    ...})