find value (and key) of an object in array (JS)

Question

I am writing a function that will iterate through an of objects to find if key:value pair exists and if so, it adds into another array (in case there are multiple matches)

The array contains objects. The function takes as argument what key and value you're looking for and then iterates through array till it finds it. As you can see, key is a variable then and my problem is I am not sure how to access object property when referring to as a variable value.

for (let i = 0; i < arr.length; i++) {
 if (arr[i].[key] == value) {
 result.push(arr[i]);
 }
}

I thought maybe putting it in [key] would help, but I was obviously wrong. I tried googling how to do it, but I guess i can't put it in words right .

Answer 1

You are confusing dot notation with bracket notation.

Remove the .; arr[i].[key] == value1 should be arr[i][key] == value.

const arr = [{
 'a': 'b'
}]
key = 'a'
value = 'b'
const result = []
for (let i = 0; i < arr.length; i++) {
 if (arr[i][key] == value) {
 result.push(arr[i]);
 }
}
console.log(result)

You can simplify the code by using filter:

const arr = [{
 'a': 'b'
}]
key = 'a'
value = 'b'
const result = arr.filter(e => e[key] == value)
console.log(result)

Answer 2

You can use ES6+ and ternary true ( && == only true action )

const arr = [{
 a: 'b'
}];
const key = 'a';
const value = 'b';
const result = [];
for (const item of arr) {
 (item[key] === value) && result.push(item)
};
console.log(result);

You can simplify the code by using filter:

const arr = [{
 a: 'b'
}];
const key = 'a';
const value = 'b';
const result = [];
for( const item of arr ) {
 ( item[key] === value ) && result.push( item )
};
console.log( result );

Answer 3

• use Array.prototype.filter()
• You should know upfront what exact property name you're willing to reference to:

const arr = [
 {name:"Evan", age:28},
 {name:"John", age:23},
 {name:"Anne", age:28},
];
const searchProp = "age";
const searchValue = 28;
const result = arr.filter((user) => user[searchProp] === searchValue);
console.log(result)

Answer 4

You are almost there, just get rid of the extra . between [i] and [key]:

for (let i = 0; i < arr.length; i++) {
 if (arr[i][key] == value) {
 result.push(arr[i]);
 }
}

However, there would be a simpler and more straight-forward way, using filter:

const result = arr.filter(obj => obj[key] == value)

Example:

const arr = [
 { a: 1, b: 1 },
 { a: 1, b: 2 },
 { a: 2, b: 1 },
 { a: 2, b: 2 }
]
const key = 'b'
const value = 1
const result = arr.filter(obj => obj[key] == value)
console.log(result)
// Output: [{ a: 1, b: 1 }, { a: 2, b: 1 }]