Having trouble deleting JavaScript object properties within a loop?

Question

Having trouble deleting JavaScript object properties within a loop?

Struggling to comprehend the behavior of this particular piece of javascript code.

const devices = searchResult.results.forEach(device => {
    const temp = Object.keys(device.fields);

    for(var property in temp) {
        if(device.fields.hasOwnProperty(property)) {
            if (!usedPropertiesAcrossModels.has(property)) {
                delete device.fields[property];
            }
        }
    }
}

Attempting to remove keys from a JavaScript object that are not part of a specific set. Despite debugging and confirming only one element in the set and 15 elements in device.fields, nothing is actually being deleted from device.fields. It's perplexing! Additionally, temp appears to be undefined until outside of the loop. The variable property remains undefined despite there being items in temp. Quite baffling!

javascript typescript

Answer 1

Answer №1

searchResult = {};
searchResult.results = [{
    fields:{
     name: 'hello',
     type:'gekko',
     random:'randomString'
      }
   }
]
usedPropertiesAcrossModels = {
  name: 'hello',
  random:'hello'
}
   

const devices = searchResult.results.forEach(device => {
                const
                temp = Object.keys(device.fields).map((property)=>{
                if(device.fields.hasOwnProperty(property)) {
                        if (!usedPropertiesAcrossModels.hasOwnProperty(property)) {
                            delete device.fields[property];
                        }
                    }
                }) 
                    
                    
   })
   console.log(searchResult)

Resolved the issue by using map instead of for in loop to get keys of the object, or using for of as suggested by Martin.

Answer 2

searchResult = {};
searchResult.results = [{
    fields:{
     name: 'hello',
     type:'gekko',
     random:'randomString'
      }
   }
]
usedPropertiesAcrossModels = {
  name: 'hello',
  random:'hello'
}
   

const devices = searchResult.results.forEach(device => {
                const
                temp = Object.keys(device.fields).map((property)=>{
                if(device.fields.hasOwnProperty(property)) {
                        if (!usedPropertiesAcrossModels.hasOwnProperty(property)) {
                            delete device.fields[property];
                        }
                    }
                }) 
                    
                    
   })
   console.log(searchResult)

Resolved the issue by using map instead of for in loop to get keys of the object, or using for of as suggested by Martin.

Answer 3

Answer №2

Using <code>const temp = Object.keys(o)

will provide you with an array of the object's keys. Instead of using a for in loop, it is recommended to use a for of loop as you need to iterate through the values, not just the keys in the temp object:

const o = { x: 10, y: 20, z: 30 };
const temp = Object.keys(o);
console.log(temp);

// This will loop through the keys in `temp`, so 0, 1, 2
for (const key in temp) {
  console.log('incorrect:', key); 
}

// This will loop through the values in `temp`, so 'x', 'y', 'z'
for (const key of temp) {
  console.log('correct:', key);
}

// Alternatively, you can also iterate using `forEach()`
temp.forEach(key => {
  console.log('correct:', key);
});

When using the for of loop, there is no need for the hasOwnProperty check.

Answer 4

Using <code>const temp = Object.keys(o)

will provide you with an array of the object's keys. Instead of using a for in loop, it is recommended to use a for of loop as you need to iterate through the values, not just the keys in the temp object:

const o = { x: 10, y: 20, z: 30 };
const temp = Object.keys(o);
console.log(temp);

// This will loop through the keys in `temp`, so 0, 1, 2
for (const key in temp) {
  console.log('incorrect:', key); 
}

// This will loop through the values in `temp`, so 'x', 'y', 'z'
for (const key of temp) {
  console.log('correct:', key);
}

// Alternatively, you can also iterate using `forEach()`
temp.forEach(key => {
  console.log('correct:', key);
});

When using the for of loop, there is no need for the hasOwnProperty check.

Having trouble deleting JavaScript object properties within a loop?

Answer №1

Answer №2

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