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How to convert pixel values to numeric values using JavaScript?

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Release： 2023-09-12 10:25:06

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如何使用 JavaScript 将像素值转换为数字值？

Converting pixel values to numeric values in JavaScript is a simple task using built-in functions such as parseInt(), parseFloat(), Number() and string methods Replace()) to complete. Each method has its own advantages and disadvantages, and the best method to use will depend on the specific requirements of the project.

When positioning and styling items on a web page, it is sometimes necessary to use both pixel values and numerical values in web development. For example, to perform a calculation or operation on a value, you might need to convert a pixel value (such as "100px") to a numeric value (such as "100"). In this article, we will discuss changing pixel values to integer values using JavaScript.

Method 1: Use parseInt() method

A built-in JavaScript function named parseInt() can be used to convert a string to an integer. Using the parseInt() method, we can convert the string value to an integer, remove the "px" unit from the string, and then convert the integer back to a numeric value.

Example

<html>
<body>
   <p id="result1"></p>
   <p id="result2"></p>
   <script>
      let pixelValue = "100px";
      document.getElementById("result1").innerHTML = "Pixel value: " + pixelValue ;
      let numberValue = parseInt(pixelValue);
      document.getElementById("result2").innerHTML = "Number value: " + numberValue;
   </script>
</body>
</html>

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Method 2: Use the replace() method

You can use the replace() method to replace the specified value with another value, which is a string method. We can change the pixel value to a numeric value by removing the "px" unit from the string using the replace() method.

Example

<html>
<body>
   <p id="result1"></p>
   <p id="result2"></p>
   <script>
      let pixelValue = "100px";
      document.getElementById("result1").innerHTML = "Pixel value: " + pixelValue ;
      let numberValue = parseInt(pixelValue.replace("px", ""));
      document.getElementById("result2").innerHTML = "Number value: " + numberValue;
   </script>
</body>
</html>

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Method 3: Use parseFloat() method

Similar to the parseInt() method, the parseFloat() method converts a string to a floating point number. The parseFloat() method can be used to convert a text value from a float to an integer value, and the "px" units can subsequently be removed.

Example

<html>
<body>
   <p id="result1"></p>
   <p id="result2"></p>
   <script>
      let pixelValue = "100.5px";
      document.getElementById("result1").innerHTML = "Pixel value: " + pixelValue ;
      let numberValue = parseFloat(pixelValue.replace("px", ""));
      document.getElementById("result2").innerHTML = "Number value: " + numberValue;
   </script>
</body>
</html>

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Method 4: Use Number() constructor

The Number() constructor creates a Number object that wraps the passed value.

Example

<html>
<body>
   <p id="result1"></p>
   <p id="result2"></p>
   <script>
      let pixelValue = "100px";
      document.getElementById("result1").innerHTML = "Pixel value: " + pixelValue ;
      let numberValue = Number(pixelValue.replace("px", ""));
      document.getElementById("result2").innerHTML = "Number value: " + numberValue;
   </script>
</body>
</html>

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To match only px units and not any substring containing the 'px' sequence, it is safer to use a regular expression as the first argument when using the Replace() method. Like this -

Example

Another important note is that these methods will return NaN (not a number) if the pixel value passed is not a string with "px" at the end. It's important to add validation in your code to handle situations like this.

<html>
<body>
   <p id="result1"></p> 
   <p id="result2"></p>
   <script>
      let pixelValue = "100px";
      document.getElementById("result1").innerHTML = "Pixel value: " + pixelValue ;
      let numberValue = parseInt(pixelValue.replace(/px/g, ""));
      document.getElementById("result2").innerHTML = "Number value: " + numberValue;
   </script>
</body>
</html>

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