How to read district city in javascript

JavaScript is a programming language widely used in web development and is popular because it is easy to learn and use. For beginners, it is very important to understand the basics of variables and data types, operators, conditional statements, loop statements, etc. in JavaScript. This article will introduce how JavaScript reads input to help readers better learn and apply this language.

1. Read text box input

In JavaScript, you can get the HTML element through the getElementById() method in the document object and read the value attribute of the element. This is useful when reading text box input. For example, the following code snippet demonstrates how to read input from a text box that contains an id attribute:

var input = document.getElementById("myInput");
var inputValue = input.value;

Where "myInput" is the value of the text box's id attribute. The variable inputValue will hold the value entered in the text box.

2. Read radio button and checkbox input

For form elements such as radio buttons and checkboxes, you can use the following code snippet to read their selections Status:

var radioBtn = document.getElementsByName("myRadioBtn");
var checkbox = document.getElementById("myCheckbox");

var radioSelectedValue;
for(var i=0; i<radioBtn.length; i++){
    if(radioBtn[i].checked){
        radioSelectedValue = radioBtn[i].value;
        break;
    }
}

var checkboxValue = checkbox.checked;

Among them, "myRadioBtn" and "myCheckbox" are the id attribute values ​​of the radio button group and check box respectively. In the reading of radio buttons, by looping through all radio button elements, only the value attribute of the selected element will be assigned to the variable radioSelectedValue. When reading the check box, the checkbox.checked property will return true or false, indicating whether the check box is selected.

3. Read drop-down list input

The drop-down list is a very common form element that provides multiple options for the user to choose. In JavaScript, you can get the value of the selected option in the following way:

var select = document.getElementById("mySelect");
var selectedOption = select.options[select.selectedIndex].value;

where "mySelect" is the id value of the drop-down list. Through the options property of the select object, you can get an HTMLCollection object containing the options provided by the drop-down list. Through the selectedIndex attribute, you can get the index value of the currently selected option. Finally, when getting the value of a selected option, just read its value property.

4. Read mouse event input

In addition to the input of form elements, JavaScript can also read user input through mouse events. For example, the following code demonstrates how to trigger an event when a button is clicked:

var button = document.getElementById("myButton");
button.addEventListener("click", function(){
    // 这里是事件触发时执行的代码
});

In this example, "myButton" is the id value of a button. A click event listener is added to the button via the addEventListener() method. When the user clicks the button, the code in the event listener will be executed.

Summary

With the above method, we can easily read various types of user input. In practical applications, we can also achieve interactive front-end effects in a variety of ways. Mastering these skills, we can apply JavaScript more flexibly to achieve better web applications.

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