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AJAX Basics

AJAX Basics. xhr = new XMLHttpRequest(); xhr.onreadystatechange = xhrHandler(); xhr.open("POST", url); xhr.send(postData); ... function xhrHandler() { if (this.readyState != 4) { return; } if (this.status != 200) { // Handle error ... return; } ...

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AJAX Basics

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  1. AJAX Basics xhr = new XMLHttpRequest(); xhr.onreadystatechange = xhrHandler(); xhr.open("POST", url); xhr.send(postData); ... function xhrHandler() { if (this.readyState != 4) { return; } if (this.status != 200) { // Handle error ... return; } ... var text = this.responseText; var document = this.responseXML; } State 4 means “done” Response available as raw text or XML CS 142 Lecture Notes: Forms

  2. Higher-Level AJAX Example Watch this element for change <%= observe_field( "userName", :frequency => 0.25, :update => "completionMenu", :url => {:action => "nameChoices"} ) %> Issue AJAX request here Replace this element’s innerHTML with response CS 142 Lecture Notes: Forms

  3. JSON Example {name: "Alice", gpa: 3.5, friends: ["Bill", "Carol", "David"]} CS 142 Lecture Notes: Forms

  4. CS 142 Lecture Notes: Forms

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