1, Preface:
The common operation methods of strings can be summarized as add, delete, modify and query. You need to know that once a string is created, it is immutable.
2, Increase
The meaning of adding is not to add content directly, but to create a copy of the string and then operate it. In addition to string splicing with + and ${}, you can also use concat.
1. concat() is used to splice one or more strings into a new string
<script>
function demoConcat() {
var str = "hello ";
var ret = str.concat("world");
console.log(ret); //hello world
console.log(str); //hello
}
demoConcat()
</script>3, Delete
Delete does not mean to delete the contents of the original string, but to create a copy of the string and then operate.
1. slice() method extracts a part of a string and returns a new string without changing the original string (taking the head but not the tail)
<script>
function demoSlice() {
var str = 'I hope the sea is calm,But there are often strong winds and bad waves.'
console.log(str.slice(1, 8)); // Output: hope the sea is calm
console.log(str.slice(4, -2)); // Output: the wind is calm, but there are often strong winds and evil
console.log(str.slice(12)); // Output: there are strong winds and bad waves.
console.log(str.slice(30)); // Output: ''
}
demoSlice()
</script>2. The substring() method returns a subset of a string from the start index to the end index, or a subset from the start index to the end of the string (including the head but not the tail)
<script>
function demoSubstring() {
var str = "I am willing to give up those young frivolous for you";
console.log(str.substring(0, 3)); //I do
console.log(str.substring(3, 7)); //Give up for you
console.log(str.substring(3, 3)); //""
console.log(str.substring(0, 15)); //I am willing to give up those young frivolous for you
}
demoSubstring()
</script>4, Change
The meaning of change is not to change the original string, but to create a copy of the string and then operate
1. replace() replaces the first place where ， and ， replaceAll() replace all
<script>
function demoReplace() {
var str = "The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?";
//Replace the first dog with monkey
// console.log(str.replace('dog', 'monkey'));
//Replace the first dog with Li Qin
var newStr = str.replace("dog", function (replacement) {
return "Li Qin"
})
console.log(newStr);
//The quick brown fox jumps over the lazy Li Qin
//If the dog reacted, was it really lazy?
// Replace all dog s with Li Qin
var newStr2 = str.replaceAll("dog", function (replacement) {
return "Li Qin"
})
console.log(newStr2);
//The quick brown fox jumps over the lazy Li Qin
//If the Li Qin reacted, was it really lazy?
}
demoReplace()
</script>2. The split() method uses the specified delimiter String to divide a String object into an array of substrings
<script>
function demoSplit() {
var str = 'The quick brown fox jumps over the lazy dog.';
var words = str.split(' ');
console.log(words);
//['The', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog.']
//Splits the target string into an array of each character
var chars = str.split('');
console.log(chars); //['T', 'h', 'e', ' ', 'q', ...'d', 'o', 'g', '.']
//Split str into an array of length 1. The only element is str itself
var strCopy = str.split();
console.log(strCopy);
// ["The quick brown fox jumps over the lazy dog."]
//Take the first five elements of the split result
chars = str.split('', 5);
console.log(chars); //['T', 'h', 'e', ' ', 'q']
}
demoSplit()
</script>3. Trim the blank space at the beginning and end of the string ({trim())
Trim off the blank space at the end of the string ()
Trim off the blank space in the string header, {trimStart()
4. toUpperCase() and toLowerCase() convert case
<script>
function demoToCase() {
var sentence = 'The quick brown fox jumps over the lazy dog.';
console.log(sentence.toUpperCase()); //THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG.
console.log(sentence.toLowerCase()); //the quick brown fox jumps over the lazy dog.
}
demoToCase()
</script>5, Check
In addition to obtaining the value of the string by index, you can also use:
1. The charAt() method returns the specified character from a string
<script>
function demoCharAt() {
var str = "I am willing to give up those young frivolous for you";
console.log(str.length); //15
for (let i = 0; i < str.length; i++) {
console.log(str.charAt(i));
}
}
// demoCharAt()
</script>2. The indexOf() method returns the index of the specified value for the first time in the String object calling it, and searches from fromIndex. If the value is not found, - 1 is returned.
<script>
function demoIndexOf() {
var str = "I am willing to give up those young frivolous for you";
var result = str.indexOf("you");
console.log(result); //4
var ret = str.indexOf("you", 5);
console.log(ret); //9
}
demoIndexOf()
</script>3. The includes() method is used to judge whether a string is contained in another string, and returns true or false according to the situation.
<script>
function demoIncludes() {
var str = "I hope the sea is calm,But there are often strong winds and bad waves."
console.log(str.includes("Langjing"));//true
console.log(str.includes("Shanghai"));//false
console.log(str.indexOf("Langjing") != -1);//true
console.log(str.indexOf("Shanghai") != -1);//false
}
demoIncludes()
</script>
https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/String