Unusual actions observed when deleting an element from an Array in Polymer 1.x

Let's say we have an array named '_arr' and I'm removing an item from it. However, before I remove the item, I log it to the console. The issue is that when I check the console log, it seems like the item has already been removed from the array. I've looked through the data system in Polymer Documentation, but I'm still confused about what might be causing this behavior.

Could it be a misunderstanding of how the data system operates, or should I be investigating another source for the problem?

EDIT: Just to clarify, '_arr' consists of an array of strings, and I'm triggering an event using:

this.fire('rmv-item' , {item: 'item content which is string'});

Below is the code snippet:

_removeItemFromArr: function(e) {

    const index = this._arr.indexOf(e.detail.item) ; 
    console.log('array before remoivng item:' , this._arr , index); //item doesn't exist

    if (index>-1) {  this.splice('_arr' , index, 1  }

    console.log('array after removing item: ' , this._arr , index); //item doesn't exist
},

Answer №1

One issue is that the problem lies in the fact that things are executing exactly as instructed: the console logs the array, it absolutely does not log the array "as it appeared at some specific past moment", rather, it logs the array in its current state when the log command is actually executed. Since the logging process is asynchronous, by the time it writes the interconnected reference and symbol table data to the console, you may have already removed data from the array. Consequently, what you see is what console.log witnesses at that moment.

If you desire an accurate snapshot of how your array looked "at the time of calling log", avoid logging the original array; instead, log a duplicate of the array using a synchronous method such as slice():

const index = this._arr.indexOf(e.detail.item); 
console.log(`array before removing item at [${index}]: ${this._arr.slice()}`);

And there you have it!

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