How to implement print preview function in javascript

With the rapid development of network technology, Internet applications are becoming more and more widespread, of which web applications have also become an indispensable part. In many web applications, the printing function is a very important function, but in different browsers and operating systems, the printing effect may be different, so we need to perform a print preview to ensure the accuracy of the printing effect. The method of implementing print preview in JavaScript has also attracted more and more attention from developers.

Pre-knowledge

Before introducing the method of implementing print preview in javascript, we need to understand some pre-knowledge:

1. window.print() method

window.print() is a method that comes with JavaScript and is mainly used to implement the printing function. After calling this method, the browser will directly start printing the current page.

2. CSS print style

In print preview, CSS style is also a very important part. We can control the layout, fonts, colors, etc. of the printed page through CSS styles.

3. Printing page size

Different devices may have different printing paper sizes, so we need to adjust the layout of the printed page according to the printing paper size of the device.

4. window.matchMedia() method

window.matchMedia() is a method that comes with javascript and is mainly used to determine the display size of the current device. We can use this method to adjust the display effects for different devices.

Implementation steps

With the foundation of pre-knowledge, we can start to introduce the method of implementing print preview in javascript.

1. Create a print button

First, we need to create a print button in the page so that users can click the button to trigger the print preview function. The button code is as follows:

<button>打印预览</button>

2. Create a print preview function

In the print button, we need to call a function named printPreview() to implement the print preview function. The function code is as follows:

function printPreview(){
  //创建新的窗口
  var printWindow = window.open('', 'printWindow', 'height=600, width=800');

  //将样式表和HTML代码添加到新窗口中
  printWindow.document.write('');
  printWindow.document.write('<link>');
  printWindow.document.write('');
  printWindow.document.write(document.getElementById('printContent').innerHTML);//printContent为需要打印的内容区域的ID，需要在页面中定义
  printWindow.document.write('');

  //设置新窗口的打印样式和相关属性
  printWindow.document.close();
  printWindow.focus();
  printWindow.print();
  printWindow.close();
}

In the above code, we first create a new window named printWindow and add the style sheet and HTML code to the window. Note that we are using a CSS style sheet called print.css here, which will only take effect when printing. Then, we set the print style and properties of the new window, and pop up the window on the screen for print preview. Finally, we close the window when we are done printing.

3. Set printing style

In the print preview function, we have added a CSS style sheet for printing. The following is the code of an example print.css file, which contains some commonly used printing styles:

/*隐藏页面中的所有元素*/
* {
  display:none;
}

/*显示需要打印的区域*/
#printContent {
  display:block;
}

/*设置打印页面的字体和颜色*/
body {
  font-family:宋体, Arial;
  font-size:16px;
  color:#000;
}

/*为打印页面进行分页*/
.my-pagebreak{
  page-break-after: always;
}

/*设置打印页面的边距*/
@media print {
  @page {
    margin:20mm 15mm !important;
  }
}

Here, we use CSS to hide all elements in the page and only display the area that needs to be printed. . At the same time, we set the font and color of the printed page, and set the pagination and margins for the page.

4. Adjust page layout

The printing paper size of different devices may be different, so we need to adjust the layout of the printed page according to the printing paper size of the device. We can use the window.matchMedia() method to determine the display size of the current device and adjust the layout of the printed page accordingly. The code is as follows:

function printPreview(){
  //创建新的窗口
  var printWindow = window.open('', 'printWindow', 'height=600, width=800');

  //根据设备的显示尺寸调整页面布局
  if (window.matchMedia('print and (max-width: 768px)').matches) {
    //设备宽度小于768px，调整页面布局
    //...
  } else if (window.matchMedia('print and (max-width: 992px)').matches) {
    //设备宽度小于992px，调整页面布局
    //...
  } else {
    //设备宽度大于等于992px，调整页面布局
    //...
  }

  //将样式表和HTML代码添加到新窗口中
  printWindow.document.write('');
  printWindow.document.write('<link>');
  printWindow.document.write('');
  printWindow.document.write(document.getElementById('printContent').innerHTML);//printContent为需要打印的内容区域的ID，需要在页面中定义
  printWindow.document.write('');

  //设置新窗口的打印样式和相关属性
  printWindow.document.close();
  printWindow.focus();
  printWindow.print();
  printWindow.close();
}

In the above code, we use the window.matchMedia() method to determine the display size of the current device and adjust the page layout according to different width ranges. According to the actual situation, we can adjust the layout of the printed page by ourselves.

Summary

Javascript's implementation of print preview can enable us to control the effect of the printed page more precisely and accurately, improving our printing experience. It should be noted that during the implementation process, we need to adjust the style and layout according to different device sizes and browser characteristics to ensure the consistency of the printing effect. At the same time, we can also use other technologies, such as CSS3’s @page rules, to further improve the control of the printing page effect.

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