jQuery

jQuery is a JavaScript Library that focuses on simplifying DOM manipulation, AJAX calls, and Event handling.

jQuery uses a format, $(selector).action() to assign an element(s) to an event. To explain it in detail, $(selector) will call jQuery to select selector element(s), and assign it to an event API called .action().

$(document).ready(function(){
  alert("Hello World!");
  $("#blackBox").hide();
});

The above code carries out the same function as the following code:

window.onload = function() {
  alert("Hello World!");
  document.getElementById("blackBox").style.display = "none";
};

Or:

window.addEventListener("load", () => {
  alert("Hello World!");
  document.getElementById("blackBox").style.display = "none";
});

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General knowledge

Technical information