How to determine what a string starts with in javascript

Judgment method: 1. Use the statement "String object.substr(0, number of comparison characters) == "Comparison characters""; 2. Use "String object.slice(0, characters number)=="Compare Characters"" statement; 3. Use the "String Object.indexOf("Compare Characters")==0" statement; 4. Use regular expressions.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

javascript determines what the string begins with

Method 1: substr() method

if("123".substr(0, 2) == "12"){
    console.log(true);
}

Method 2: slice() method

if("123".slice(0,2) == "12"){
    console.log(true);
}

Method 3: indexOf() method

if("123".indexOf("12") == 0) {
    console.log(true);
}

Method 4: Regular

if("123".search("12") != -1) {
    console.log(true);
}if(new RegExp("^12.*$").test(12)) {
    console.log(true);
}if("12".match(new RegExp("^12.*$"))) {
    console.log(true);
}

[Recommended learning: javascript advanced tutorial]

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