Difference between var.method() and method(var)?

Question

Wondering why something like var numWidth = boxWidth.parseInt(); doesn't work compared to the accepted var numWidth = parseInt(boxWidth)?

It seems like one could evaluate var numWidth = boxWidth.toUpperCase(), but not the previous example.

Any good explanations?

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>JavaScript Foundations: Parsing Numbers From Strings</title>
    <link rel="stylesheet" href="core.css">
    <script>
      var boxWidth = "640px";
      var boxHeight = "480px";
      var numWidth = boxWidth.parseInt();
      var numWidth = parseInt(boxWidth);

    </script>
  </head>
  <body>
    <h1>JavaScript Foundations</h1>
    <h2>Parsing Numbers From Strings</h2>
    <script src="viewer.js"></script>
  </body>
</html>

Answer 1 · 2015-03-11T11:46:09Z

March 11, 2015 11:46am

When a method uses a dot operator (boxWidth.parseInt();, in your example), it means it is part of an Object prototype. i.e. an Object was created that has one or more various methods which do something relating to that Object. This is evident in the commonly used Array methods, such as Array.push()) - you create an Array and use the push() method to add one item to your Array.

Some methods are stand-alone functions, such as parseInt(). This is a global function, meaning it is packaged with JavaScript. These types of methods are still specific (they do a task), but don't really fit in with an Object type.

toUpperCase is a method on a String Object so if boxWidth is NOT a String (e.g. a Number) then an error will occur.

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Owen O

Owen O

Difference between var.method() and method(var)?

1 Answer

Sean T. Unwin

Sean T. Unwin