string object in JavaScript_javascript skills
1.String: Stores a string and provides the properties and methods needed to process strings.
1. Create String object: explicit and implicit
<DOCTYPE html>
<html>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<head>
<title>js函数</title>
</head>
<script type="text/javascript">
//申明String对象的两种方式：显式和隐式申明
//1.隐式
var myString="abc";
document.write(myString+"<br/>");
//2.显式
var myString2=new String("abc");
document.write(myString2+"<br/>");
</script>
<body>
</body>
</html>
*Explicitly and implicitly declared String objects have different types: the implicitly declared string object has type string, while the explicitly declared string object has type object.
*The real difference between explicit and implicit string creation is that if you want to reuse the same string, explicitly creating the string is more efficient;
* Explicitly creating strings also helps the JavaScript interpreter confuse numbers and strings;
2. Methods of using String objects
String object has many methods, only two are discussed here. indexOf() and substring() methods; pay attention to case.
*What you need to know: JavaScript strings are composed of characters. Each of these characters has an index. The index is 0-based, so the first position has an index of 0; the second position has an index of 1, and so on.
*The method indexOf() finds and returns the index position of the beginning of the substring. If the element being searched does not exist, it returns -1, otherwise it returns the index where the character is located. (lastIndexOf returns the position of the end of the substring)
Write an example below to determine whether the email address entered by the user number contains the @ symbol:
<DOCTYPE html>
<html>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<head>
<title>js函数</title>
</head>
<script type="text/javascript">
//让用户输入Email地址，检查输入是否包含@符号
//使用prompt方法，获取用户输入的Email地址，检查是否包含@符号，使用indexof返回@符号的索引
var userInput=prompt("Please enter your email address","Email");
if(Number(userInput.indexOf("@"))==-1)
{
document.write("对不起，您输入的Email不合法");
}
else
{
document.write("恭喜您，您输入的Email通过验证");
}
</script>
<body>
</body>
</html>
substring() method uses the index of the starting position and ending position of the string as parameters to intercept a string from another string. You can return all strings from the first index to the end of the string without using the second parameter. For example, if we want to intercept all characters from the third to the sixth character, we can write like this:
<DOCTYPE html>
<html>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<head>
<title>js函数</title>
</head>
<script type="text/javascript">
//从起始位置，到结束位置
var myhello="Hello Javascript World";
var newMyhello= myhello.substring(0);
document.write(newMyhello+"<br/>");
//从第三个字符到第六个字符
var myhello="Hello Javascript World";
var newMyhello= myhello.substring(2,5);
document.write(newMyhello+"<br/>");
</script>
<body>
</body>
</html>
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