check if jquery is defined javascript code example

Example 1: check if jquery is installed

if (typeof jQuery == "undefined") {
  alert("JQuery is not installed");
} else {
  alert("JQuery is installed correctly!");
}

Example 2: test if jquery works

/* Answer to: "test if jquery works" */

window.onload = function() {
    if (window.jQuery) {  
        // jQuery is loaded  
        console.log("jQuery has loaded!");
    } else {
        // jQuery is not loaded
        console.log("jQuery has not loaded!");
    }
}