Modify part of object stored in an array in Ionic Storage

Question

I'm trying to modify a part if an object stored in an array in Ionic Storage. I would like to change the data b to "111" when a === '4'

key : "array"
value : "[{"a":"1","b":"2","c":"3"},{"a":"4","b":"5","c":"6"},{"a":"7","b":"8","c":"9"}]"

modifyArray() {
    // tslint:disable-next-line: forin
    for (let i in this.array) {
      this.storage.get('array').then(res => {
        let y = JSON.parse(res);
        let r = JSON.stringify(JSON.parse(res)[i]);

        console.log('y : ' + JSON.stringify(y));
        console.log('r : ' + r);

        if (JSON.parse(r).a === '4') {
          JSON.parse(r).b = '111';
        }
        this.storage.set('array', JSON.stringify(JSON.parse(r)));
      });
    }
  }

After the execution of my function, I've got :

key : "array"
value : "{"a":"7","b":"8","c":"9"}"

I would like to obtain :

key : "array"
value : "[{"a":"1","b":"2","c":"3"},{"a":"4","b":"111","c":"6"},{"a":"7","b":"8","c":"9"}]"

Seems to me that parsing once and stringifying once should be sufficient. Don't know why you have half a dozen parse/stringify operations in your code. Also unclear why you need the outer loop. — Robby Cornelissen
– Robby Cornelissen, Commented Sep 20, 2019 at 8:27

Pankaj Sati · Accepted Answer · 2019-09-20 09:10:11Z

1

Avoid unnecessary multiple parse and stringify calls. Simply, parse your value once and then you can access them using ['a'] or .a

Here is a working example of what you wanted to achieve:

let parsedValue = JSON.parse(res);
console.log('After parsing');
console.log(parsedValue);

for (let eachItem of parsedValue)
{

  if (Number(eachItem['a']) == 4)
  {
    eachItem['b'] = "111";
    console.log('Changed B' + eachItem['b']);
  }
}

console.log('After Changing');
console.log(parsedValue);

answered Sep 20, 2019 at 9:10

Pankaj Sati

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Comments

Shankar_programmer · Accepted Answer · 2019-09-20 10:47:33Z

In your code only last execution of the for loop result will be stored. You need to create an empty array and need to push after every execution. once all execution of loop gets finished you can able to store in ionic local storage.

This can be acheived by following two methods.

Method 1:

modifyArray() {
    var final_push = [];
    for (let i in this.array) {
      this.storage.get('array').then(res => {        
        let y = JSON.parse(res);        
        if (y[i]['a'] === '4') {
          y[i]['b'] = '111';
        }
        final_push.push(y);        
      });
    }
    this.storage.set('array', JSON.stringify(JSON.parse(final_push)));
}

Method 2:

modifyArray() {
    var final_push = [];
    for (let i in this.array) {
      this.storage.get('array').then(res => {        
        let y = JSON.parse(res);        
        if (y[i]['a'] === '4') {
          y[i]['b'] = '111';
        }
        final_push.push(y);  
        if(i == this.array.length - 1){
          this.storage.set('array', JSON.stringify(JSON.parse(final_push)));
        }
      });
    }

}

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