Some uncommon and practical functions in javascript

It’s been 996 for almost two months. I haven’t written anything for more than a month. Today I will record some usages in JavaScript that are convenient but not commonly used

1. ~indexOf()

Generally speaking , to determine whether a string contains a substring, you can use indexOf(subString) > -1 to represent

We can also use ~indexOf(subString) to represent

indexOf() returns -1 to mean no, returns 0 And the number greater than 0 means that the result of ~-1 is 0, which is equivalent to false

in if. 0 and greater than 0 are numbers that are not 0 after the ~ operation, which is equivalent to true

2 in if. ~~

                                                                                                                                                                                                                                                                    ~ ;>0 n|0

Of course, there is a limitation in using these algorithms for rounding, that is, the range of numbers can only be used within the range of 32-bit binary numbers, that is, the numbers must be between -2147483648 ~ 2147483647. This is also a number of plus or minus 2 billion. Under normal circumstances, there is no problem.

3. This is a problem and makes me a little confused.

The method of toFixed is to round the Number to a number with specified decimal places.

The Math.round method can round the number to the nearest integer

But for -4.5.toFixed(0) and Math.round(-4.5), one returns -5 and the other returns -4.

Why is this, it makes me very confused, can anyone explain to me