javascript - In map implementation in js, var len = O.length >>> 0;

Question

if (!Array.prototype.map) {
  Array.prototype.map = function(callback, thisArg) {
    var T, A, k;
    if (this == null) {
      throw new TypeError(" this is null or not defined");
    }
    var O = Object(this);
    var len = O.length >>> 0;
    // 3.如果callback不是函数,则抛出TypeError异常.
    if (Object.prototype.toString.call(callback) != "[object Function]") {
      throw new TypeError(callback + " is not a function");
    }
    if (thisArg) {
      T = thisArg;
    }
    A = new Array(len);
    k = 0;
    while(k < len) {
      var kValue, mappedValue;
      if (k in O) {
        kValue = O[ k ];
        mappedValue = callback.call(T, kValue, k, O);
        A[ k ] = mappedValue;
      }
      k++;
    }
    return A;
  };      
}

var len = O.length >>> 0; What is the purpose of the bit operators here

Answer 1

Personal understanding:

Because although this map method is on the prototype of Array, when it is actually called, this is not necessarily of Array type, and the length cannot be guaranteed. After adding bit operations, the uncertain value can be converted into Number.

1 >>> 0 // 1
undefined >>> 0 // 0
null >>> 0 // 0
'string' >>> 0 // 0

Answer 2

Convert any JS value into a number without NaN

Answer 3

1. All non-numeric values ​​are converted to 0

2. All numbers greater than or equal to 0 take the integer part