JavaScript data type example sharing_basic knowledge

We introduced the data types of JavaScript earlier. Today we will review them through some examples. I hope everyone can learn new things.

Copy code The code is as follows: //1. Boolean type //2. Number type //3. String type //Boolean types are easily confused with basic types, so it is recommended that you never use Boolean objects. //Number is a reference type corresponding to a number var numberObj = new Number(10); //Rewrite the toString method. The parameter passed in is the string type that tells it to put back the decimal number var num = 10; alert(num.toString());//"10" alert(num.toString(2));//"1010" alert(num.toString(8));//"12" alert(num.toString(10));//"10" alert(num.toString(16));//"a" //The toFixed() method is a string representation method that returns a value with specified decimal places, and has a rounding function var num = 10; num.toFixed(2);//"10.00" //toExponential() exponential notation method, accepts a parameter indicating the number of decimal places in the output result var num = 10; alert(num.toExponential(1));//"1.0e 1" //However, there is no need to use exponential notation for such a small number. If you want to get the most appropriate format for a certain value, you should use //toPrecision() method, this method may return fixed size (fixed) format or exponential (exponential) format //Accepts a parameter that represents the number of digits in all digits of the value (excluding the exponent part). var num = 99; alert(num.toPrecision(1));//1e 2, 1e 2 represents 100, because the exponent cannot represent 99, so it is rounded up to 100 alert(num.toPrecision(2));//"99" alert(num.toPrecision(3));//"99.0" //String object, the methods of String object can also be accessed in all basic strings. //1. Character operation methods: charAt(), charCodeAt(). Each parameter accepts a character position based on position 0 var stringValue = "Hello world!"; stringValue.charAt(1);//The second position of "e" is "e" StringValue.charCodeAt(1);//"101" The character code of the second position "e" is "101" //2. String operation methods concat (concatenated characters), slice (index, index), substring (index, index), substr (index, length). index: position, length: length var str1 = "hello"; alert(str1.concat(" word"));//Hello world alert(str1.concat(" word", "!"));//Hello world! var stringValue = "Hello world!"; alert(stringValue.slice(3));//lo world alert(stringValue.substring(3));//lo world alert(stringValue.substr(3));//lo world alert(stringValue.slice(3, 7));//lo w alert(stringValue.substring(3, 7));//lo w alert(stringValue.substr(3, 7));//lo worl This 7 represents the intercepted length //3. String position methods indexOf() and lastIndexOf() //These two methods search for the given string from the specified string, and then return the position of the string. If not found, return -1. //The difference between these two methods is that one searches the string backward from the beginning of the string, while lastIndexOf searches the string forward from the end of the string. //Both methods have an optional parameter (start searching from the specified position) var stringValue = "hello word"; alert(stringValue.indexOf("o"));//4 alert(stringValue.lastIndexOf("o"));//7 //You can call indexOf or lastIndexOf in a loop to find the specified string var stringValue = "wo de wei lai bu shi meng!wo men you geng hao de ming tian!"; var positions = []; var pos = stringValue.indexOf("e"); while (pos > -1) { positions.push(pos); pos = stringValue.indexOf("e", pos 1); } alert(positions);//4, 7, 22, 33, 38, 47 //4. The trim() method will create a copy of the string and delete all leading and trailing spaces. var stringValue=" hello word "; alert(stringValue); alert(stringValue.trim()); //5. String case conversion method //toLowerCase, toLocalLowerCase, toUpperCase, toLocalUpperCase var stringValue="hello word"; alert(stringValue.toLocaleUpperCase());//This method is safer alert(stringValue.toUpperCase()); alert(stringValue.toLocaleLowerCase());//This method is safer alert(stringValue.toLowerCase()); //6. String matching method replace() //This method accepts two parameters. The first parameter is a regular expression or string, and the second parameter is a string or a function var text="cat,bat,sat,fat"; var result=text.replace("at","ond");// alert(result);//"cond,bond,sond,fond" var result=text.replace(/at/g,"ond");// alert(result);//"cond,bond,sond,fond" var text="cat,bat,sat,fat"; result=text.replace(/(.at)/g,"word ($1)"); alert(result); //The second parameter of replace can also be a function function htmlEscape(text) { //The function has three parameters: 1. Pattern matching item 2. The position of the pattern matching item in the character 3. Original string return text.replace(/[<>"&]/g,function(match,index,text){ switch (match){ case " return " case ">": return ">"; case "&": return "&"; case """: return """; } }); } alert(htmlEscape(" Hello World!

")); // Hello World!

//localCompare() compares two strings. A.localCompare("B") //If string (A) comes before the string parameter (B) in the alphabet, this returns a negative number (-1) //If the string is equal to the string parameter, return 0 //If the string (A) is after the string parameter (B) in the alphabet, return a positive number (1) var stringValue="f"; alert(stringValue.localeCompare("d"));//1 alert(stringValue.localeCompare("f"));//0 alert(stringValue.localeCompare("z"));//-1 //fromCharCode This static method performs the opposite operation to charCodeAt alert(String.fromCharCode(104,101,108,108,111));//"hello" //7. It is recommended not to use the html method. END

Have you guys gained a new understanding of JavaScript data types? I hope you all like it.

JavaScript data type example sharing_basic knowledge

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