Set (a==1 && a==2 && a==3) to true

Today encountered an interesting problem, hereby record

leta = ? ; (a==1 && a==2 && a==3) {
    console.log('yes')}Copy the code

The valueOf a can be changed by rewriting the num method. The valueOf a can be changed by rewriting the num method. The valueOf a can be changed by rewriting the num method.

let a = {
  val: 1.toString() {
    returna.val++; }}Copy the code

This can also be done with Object.defineProperty

let num = 0;
Object.defineProperty(window.'a', {
  get() {
    return++num; }})Copy the code

conclusion

1. When using object comparisontoStringThe method of
2. usingObject.definePropertyhijackedJSThe object’sgetter