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Please forgive me for asking such unreasonable and irregular questions.

Out of curiosity, I modified the Object.prototype.hasOwnProperty method with the following code, hoping to output the value of the object calling this method.

Code 1

Object.prototype.hasOwnPropertyOld = Object.prototype.hasOwnProperty;
Object.prototype.hasOwnProperty = function (data) {
  console.log(this);
  return this.hasOwnPropertyOld(data);
};
let a = { a: 1, b: 2 };
a.hasOwnProperty("a");
// out:
// {a: 1, b: 2}
// true
a.hasOwnProperty("c");
// out:
// {a: 1, b: 2}
// false

However, the following code seems to cause the page to crash in some cases.

I added a breakpoint for debugging in the Google Chrome Devtool, and did not find out why it crashed, but in the Devtool console, it seems to work normally.(Unfortunately, I can’t provide webpage code that reproduces this problem, but it does happen)

I checked the information and re-modified the Object.prototype.hasOwnProperty method again, see code 2, but it has not been verified at present.

Code 2

let hasOwnPropertyOld = Object.prototype.hasOwnProperty;
Object.prototype.hasOwnProperty = function (params) {
  console.log(this);
  return hasOwnPropertyOld.call(this, params);
};

What kind of situation, what kind of data Code 1 will crash the page?

I think I know the reason, the browser I use may not comply with certain specifications, code 1 in a program's built-in browser, will be stuck, but it is normal in Google Chrome I guess that different browsers execute the above code in different ways, which may lead to a stuck Object.prototype.hasOwnPropertyOld pointing to Object.prototype.hasOwnProperty When running, recursion and endless loops will occur. The following code will also cause a program error

Object.prototype.hasOwnPropertyOld = Object.prototype.hasOwnProperty;
Object.prototype.hasOwnProperty = function (data) {
  console.log(this);
  return this.hasOwnPropertyOld(data);
};
let a = { a: 1, b: 2};
a.hasOwnProperty("a");
// out:
// {a: 1, b: 2}
// true
a.hasOwnProperty("c");
// out:
// {a: 1, b: 2}
// false

let b = {
  a: 1,
  b: 2,
  hasOwnProperty: (data) => {
    while (true) {
      console.error("error");
    }
  },
};

b.hasOwnProperty("a");

So I suggest to modify Object.prototype.hasOwnProperty through code 2

Ucc Mtr
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    Hard to say, but one idea is that console maybe sometimes uses it depending on what gets logged, so maybe causing an infinite loop. Maybe put an infinite loop check in.. – Keith Jun 20 '20 at 19:02
  • @Keith not an "infinite loop" check, more accurately a [reentrancy](https://en.wikipedia.org/wiki/Reentrancy_(computing)) check. – Bergi Jun 20 '20 at 20:24
  • What exactly do you mean by "*seems to cause the page to crash*"? Which page, and what happens? How can we reproduce the issue? – Bergi Jun 20 '20 at 20:25
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    A clear problem with code1 is that you're creating an enumerable property on `Object.prototype`. Have a look at [how to define method in javascript on Array.prototype and Object.prototype so that it doesn't appear in for in loop](https://stackoverflow.com/q/13296340/1048572). – Bergi Jun 20 '20 at 20:27

0 Answers0