JavaScript-这些值分配（使用| =作为运算符）是什么意思？

Question

Today I have seen these code-snippet:

  /**
     * @param src: any variable of any type
     * @param html: output format (true|false); default = false
     * @param level: (internal, don't use)
     *
     * @return string: formatted output
     */
    function showObj(src, html, level) {
      level |= 0;

Complete script: https://codereview.stackexchange.com/questions/123283/helper-function-to-format-output-any-type-of-variable

What is the value-assignment with |= ( in "level |= 0" ) ?

I haven't seen it anywhere before and can't find anything about it.

Answer 1

That( | ) is a bit wise or operator , It normally used in situations where the decimal points of a number has to be truncated.

var level = 2.444434;
level |= 0; // level = level | 0;
console.log(level) // 2

Answer 2

The bitwise OR assignment operator uses the binary representation of both operands, does a bitwise OR operation on them and assigns the result to the variable.

Live Demo

 var bar = 5; bar |= 2; // 7 alert(bar) 

Source