How to use the bitwise NOT operator in JavaScript_Basic knowledge

~: The bitwise NOT operator is represented by a tilde (~). The result of performing the bitwise NOT operation is the complement of the returned value.

Copy code The code is as follows:

var num1 = 3; // My lucky number is 3
var num2 = ~(num1);
console.log(num2) // "-4"
var num3 = -3;
var num4 = ~(num3);
console.log(num4) // "2"
console.log(~(0)) // "-1"

Yes, now we know the principle of ~ operator . Are you happy? . . . Not happy, although I have read this chapter many times. . . Because I have never used it, I am really ashamed. Where do you think this operator can be used? kindness. . . Think for a moment and put a piece of code from a colleague:

Copy the code The code is as follows:

if (~ item[search_key].toLowerCase().indexOf(query)) {
                                                                                                                                                                                                           . 🎜>
Copy code

The code is as follows:

if( str.indexOf(query) != -1 ) or if( str.indexOf(query) >= 0)Principle analysis: The final value obtained through str.indexOf(query) is nothing more than two types: 1. str contains query characters string, the value is 0 or a positive integer, at this time: !!(~str.indexOf(query)) === true (or convert Boolean(~str.indexOf(query)) === true)

2. If srt does not contain the query string, the value is -1. At this time: !!(~str.indexOf(query)) === false

So by adding a ~, indexOf can be well adjusted The query results are judged. It's so refreshing and I no longer have the trouble of dandruff. . Ha ha!
Finally, let’s analyze the efficiency. The impression is that the efficiency of bitwise operations should be higher than that of operators. Here is a piece of code:

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The code is as follows:

var str = "hutaoer go go go !!!! My lucky number is 33!!"; var query = 33; var timeStart1 = new Date() - 0; for(var i = 0; i < 100000000; i ) {        ~str.indexOf(query)    }

    var timeEnd1 = new Date() - 0;

    console.log('~ cost time:' (timeEnd1 - timeStart1));
// ~ cost time:9954 Number of loops: 10000000
// ~ cost time:104 Number of loops: 100000
var timeStart2 = new Date() - 0;
for(var j = 0 ; j < 100000000; j ) {
str.indexOf(query) >= 0
}
var timeEnd2 = new Date() - 0;
console.log('>= cost time:' (timeEnd2 - timeStart2));
// >= cost time:10120 Number of loops: 10000000


Program update: The original test code remains unchanged above the dividing line. The code is as follows:




Copy the code

The code is as follows:

    var str = "hutaoer go go go!!!!! My lucky number is 33!!";
    var query = 33;
    var timeStart1 = new Date() - 0;
    for(var i = 0; i < 1000000; i ) {
        ~str.indexOf(query)
    }
    var timeEnd1 = new Date() - 0;
    console.log('~ cost time:' (timeEnd1 - timeStart1));
    //  循环1000000次  127ms
    var timeStart2 = new Date() - 0;
    for(var j = 0; j < 1000000; j ) {
        str.indexOf(query) >= 0
    }
    var timeEnd2 = new Date() - 0;
    console.log('>= cost time:' (timeEnd2 - timeStart2));
    // 循环1000000次 101ms
    var timeStart3 = new Date() - 0;
    for(var k = 0; k < 1000000; k ) {
        Boolean(~str.indexOf(query))
    }
    var timeEnd3 = new Date() - 0;
    console.log('add Boolean cost time:' (timeEnd3 - timeStart3));
    // 循环1000000次 129ms
    var timeStart4 = new Date() - 0;
    for(var k = 0; k < 1000000; k ) {
        !!(~str.indexOf(query))
    }
    var timeEnd4 = new Date() - 0;
    console.log('add !! cost time:' (timeEnd4 - timeStart4));
    // 循环10000000次 103ms
   

其实，对于一次运算本身来说，相差无几，只是在循环次数过大，比如超过了10000000次，效率才会有一些差距。
【更新 2013.10.27 17:28】通过修改后的测试，我们可以发现，“按位非”这中写法也许并非是效率最高的，表现最好的居然是我以前常用的写法，采用比较运算符。这确实让我很吃惊。有时候，人往往容易被常识，表象所迷惑，但亲自去尝试后，或许会有不一样的发现或得出其他的结果。今天，我算吸取教训了。
在评论中，同学们都比较反对这种非常见的写法，毕竟这些技巧可能会给阅读代码的同学造成困扰。如果不知道原理的话，甚至让人费解。或许，直接用一些简单的逻辑和常见的运算符，会是更好的选择？你们觉得呢？
因此平时写代码的时候，用哪种写法都可以。但是希望我们能将这些技巧记住，关键时刻或许就能派上用场。