Array.prototype.map can be used to map one array to another.

var names = employees.map(function(i) {
  return i.name;
});

names is now an array containing the name-properties of the objects.

Here is a shorter way of achieving it:

let result = objArray.map(a => a.foo);

OR

let result = objArray.map(({ foo }) => foo)

You can also check Array.prototype.map().

If your id's are unique you can use find()

var frequencies = [{"id":124,"name":"qqq"},{"id":589,"name":"www"},{"id":45,"name":"eee"},{"id":567,"name":"rrr"}];
                  
var result = frequencies.find(function(e) {
  return e.id == 45;
});

console.log(result)

Simple add ?.age to your found variable.

var obj = [
    { name: 'Max', age: 23 },
    { name: 'John', age: 20 },
    { name: 'Caley', age: 18 }
];
 
var found = obj.find(e => e.name === 'John')?.age; // Using ?. incase value isnt found.
console.log(found);

You also mention you need it as a string, you can do achieve by wrapping the found var in the String function like so...

var obj = [
    { name: 'Max', age: 23 },
    { name: 'John', age: 20 },
    { name: 'Caley', age: 18 }
];
 
var found = String(obj.find(e => e.name === 'John')?.age);
console.log(found);

As @ashish-singh suggested you should use Object.entries

Methods:[{"foo": "walk"}, {"bar":"run"}],

getMethodList(){
  return this.state.Methods.map((item, index) => (
    <div key={index}>
      <input type="radio"
        name="Method"
        value={Object.entries(item)[0][0]} 
        onChange={this.handleMethodSelect}
     />
     {Object.entries(item)[0][1]} 
    </div>
  ))
}

Let me say that this is an unusual way of using object, without knowing the key and using the key as a value. Probably you should use something like this:

Methods:[{ key: "foo", value: "walk"}, { key: "bar", value:"run"}],

getMethodList(){
  return this.state.Methods.map((item, index) => (
    <div key={index}>
      <input type="radio"
        name="Method"
        value={item.key} 
        onChange={this.handleMethodSelect}
     />
     {item.value} 
    </div>
  ))
}

You don't need multiple for loop for this. You can do this using one forEach() loop and template literal like:

var customerData = [{ customerName: "Jay", Purchased: "phone", Price: "€200" },
  { customerName: "Leo", Purchased: "car", Price: "€2000" },
  { customerName: "Luk", Purchased: "Xbox", Price: "€400" },
];

function getValue() {
  customerData.forEach(x => {
    console.log(`Dear ${x.customerName} thank you for purchase of a ${x.Purchased} for the price of ${x.Price}`)
  })
}

getValue();

You need to use map to convert an array of objects into an array of values

const SelectedOptions = [
{
    label: 'label1',
    value: '1',
},
{
    label: 'label2',
    value: '2',
}
];

result = SelectedOptions.map(option => option.value);

console.log(result);

I know this question is old, but no one has mentioned a native solution yet. If you're not trying to support archaic browsers (which you shouldn't be at this point), you can use array.filter:

var arr = [];
arr.push({name:"k1", value:"abc"});
arr.push({name:"k2", value:"hi"});
arr.push({name:"k3", value:"oa"});

var found = arr.filter(function(item) { return item.name === 'k1'; });

console.log('found', found[0]);

Check the console.

You can see a list of supported browsers here.

In the future with ES6, you'll be able to use array.find.