Example of how to exit the loop in Array.forEach in js

forEach() Method

Syntax: array.forEach(callback(currentvalue,index,arr),thisValue)

in

callback is a function executed for each element in the array, which can accept 1-3 parameters:

• The currentvalue parameter represents the current element of the array, a required parameter
• The index parameter represents the current element index, optional parameter
• The arr parameter indicates the array to which the current element belongs. It is an optional parameter.

thisValue represents the this point when the callback function callback() is executed. Optional parameter. When not written, the default is to point to the window global

Example

    var arr = [1, 3, 5, 13, 2];
    var res = arr.forEach(function(item,index) {
        console.log(`The ${index+1}th element of the array is ${item}`);
    })
    console.log(res); //The return value of forEach is undefined,

Running results:

How to jump out of the loop in Array.forEach in js

forEach cannot jump out of the loop through break or return. The general way to jump out of the loop is to throw an exception:

 try {
   let array = [1, 2, 3, 4]
   array.forEach((item, index) => {
     if (item === 3) {
       throw new Error('end')//If an error occurs, the loop will be exited} else {
       console.log(item)
     }
   })
 } catch (e) {
 }

This way of writing is actually very troublesome.

Solution:

1. Use every instead:

let array = [1, 2, 3, 4]
array.every((item, index) => {
  if (item === 3) {
    return true
  } else {
    console.log(item)
  }
})

2. Write one yourself 😁

//Array traversal that can jump out of the loop Array.prototype.loop = function(cbk) {
  //Judge whether the current array is empty if (this?.length) {
    for (let i = 0; i < this.length; i++) {
      let stop = cbk(this[i], i, this)
      //Judge whether to stop the loop if (stop) {
        break
      }
    }
  }
}


let array = [1, 2, 3, 4]
array.loop ((item, index) => {
  if (item === 3) {
    return true
  } else {
    console.log(item)
  }
})

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