I want to cycle through the objects contained in an array and change the properties of each one. If I do this:
for (var j = 0; j < myArray.length; j++){
console.log(myArray[j]);
}
The console should bring up every object in the array, right? But in fact it only displays the first object. if I console log the array outside of the loop, all the objects appear so there's definitely more in there.
Anyway, here's the next problem. How do I access, for example Object1.x in the array, using the loop?
for (var j = 0; j < myArray.length; j++){
console.log(myArray[j.x]);
}
This returns "undefined." Again the console log outside the loop tells me that the objects all have values for "x". How do I access these properties in the loop?
I was recommended elsewhere to use separate arrays for each of the properties, but I want to make sure I've exhausted this avenue first.
Thank you!
Use forEach its a built-in array function. Array.forEach()
:
yourArray.forEach(function (arrayItem) {
var x = arrayItem.prop1 + 2;
console.log(x);
});
Some use cases of looping through an array in the functional programming way in JavaScript:
const myArray = [{x:100}, {x:200}, {x:300}];
myArray.forEach((element, index, array) => {
console.log(element.x); // 100, 200, 300
console.log(index); // 0, 1, 2
console.log(array); // same myArray object 3 times
});
Note: Array.prototype.forEach() is not a functional way strictly speaking, as the function it takes as the input parameter is not supposed to return a value, which thus cannot be regarded as a pure function.
const people = [
{name: 'John', age: 23},
{name: 'Andrew', age: 3},
{name: 'Peter', age: 8},
{name: 'Hanna', age: 14},
{name: 'Adam', age: 37}];
const anyAdult = people.some(person => person.age >= 18);
console.log(anyAdult); // true
const myArray = [{x:100}, {x:200}, {x:300}];
const newArray= myArray.map(element => element.x);
console.log(newArray); // [100, 200, 300]
Note: The map() method creates a new array with the results of calling a provided function on every element in the calling array.
const myArray = [{x:100}, {x:200}, {x:300}];
const sum = myArray.map(element => element.x).reduce((a, b) => a + b, 0);
console.log(sum); // 600 = 0 + 100 + 200 + 300
const average = sum / myArray.length;
console.log(average); // 200
const myArray = [{x:100}, {x:200}, {x:300}];
const newArray= myArray.map(element => {
return {
...element,
x: element.x * 2
};
});
console.log(myArray); // [100, 200, 300]
console.log(newArray); // [200, 400, 600]
const people = [
{name: 'John', group: 'A'},
{name: 'Andrew', group: 'C'},
{name: 'Peter', group: 'A'},
{name: 'James', group: 'B'},
{name: 'Hanna', group: 'A'},
{name: 'Adam', group: 'B'}];
const groupInfo = people.reduce((groups, person) => {
const {A = 0, B = 0, C = 0} = groups;
if (person.group === 'A') {
return {...groups, A: A + 1};
} else if (person.group === 'B') {
return {...groups, B: B + 1};
} else {
return {...groups, C: C + 1};
}
}, {});
console.log(groupInfo); // {A: 3, C: 1, B: 2}
const myArray = [{x:100}, {x:200}, {x:300}];
const newArray = myArray.filter(element => element.x > 250);
console.log(newArray); // [{x:300}]
Note: The filter() method creates a new array with all elements that pass the test implemented by the provided function.
const people = [
{ name: "John", age: 21 },
{ name: "Peter", age: 31 },
{ name: "Andrew", age: 29 },
{ name: "Thomas", age: 25 }
];
let sortByAge = people.sort(function (p1, p2) {
return p1.age - p2.age;
});
console.log(sortByAge);
const people = [ {name: "john", age:23},
{name: "john", age:43},
{name: "jim", age:101},
{name: "bob", age:67} ];
const john = people.find(person => person.name === 'john');
console.log(john);
The Array.prototype.find() method returns the value of the first element in the array that satisfies the provided testing function.
for (var j = 0; j < myArray.length; j++){
console.log(myArray[j].x);
}
Here's an example on how you can do it :)
var students = [{
name: "Mike",
track: "track-a",
achievements: 23,
points: 400,
},
{
name: "james",
track: "track-a",
achievements: 2,
points: 21,
},
]
students.forEach(myFunction);
function myFunction(item, index) {
for (var key in item) {
console.log(item[key])
}
}
Looping through an array of objects is a pretty fundamental functionality. This is what works for me.
var person = [];
person[0] = {
firstName: "John",
lastName: "Doe",
age: 60
};
var i, item;
for (i = 0; i < person.length; i++) {
for (item in person[i]) {
document.write(item + ": " + person[i][item] + "<br>");
}
}
myArray[j.x]
is logically incorrect.
Use (myArray[j].x);
instead
for (var j = 0; j < myArray.length; j++){
console.log(myArray[j].x);
}
It's really simple using the forEach method since ES5+. You can directly change each property of each object in your array.
myArray.forEach(function (arrayElem){
arrayElem = newPropertyValue;
});
If you want to access a specific property on each object:
myArray.forEach(function (arrayElem){
arrayElem.nameOfYourProperty = newPropertyValue;
});
Here's another way of iterating through an array of objects (you need to include jQuery library in your document for these).
$.each(array, function(element) {
// do some operations with each element...
});
This would work. Looping thorough array(yourArray) . Then loop through direct properties of each object (eachObj) .
yourArray.forEach( function (eachObj){
for (var key in eachObj) {
if (eachObj.hasOwnProperty(key)){
console.log(key,eachObj[key]);
}
}
});
Array object iteration, using jQuery, (use the second parameter to print the string).
$.each(array, function(index, item) {
console.log(index, item);
});
Accepted answer uses normal function. So posting the same code with slight modification using arrow function on forEach
yourArray.forEach(arrayItem => {
var x = arrayItem.prop1 + 2;
console.log(x);
});
Also in $.each you can use arrow function like below
$.each(array, (item, index) => {
console.log(index, item);
});
You can use a for..of loop to loop over an array of objects.
for (let item of items) {
console.log(item); // Will display contents of the object inside the array
}
One of the best things about for..of
loops is that they can iterate over more than just arrays. You can iterate over any type of iterable, including maps and objects. Make sure you use a transpiler or something like TypeScript if you need to support older browsers.
var c = {
myProperty: [
{ name: 'this' },
{ name: 'can' },
{ name: 'get' },
{ name: 'crazy' }
]
};
c.myProperty.forEach(function(myProperty_element) {
var x = myProperty_element.name;
console.log('the name of the member is : ' + x);
})
This is one of the ways how I was able to achieve it.
const jobs = [
{
name: "sipher",
family: "sipherplus",
job: "Devops"
},
{
name: "john",
family: "Doe",
job: "Devops"
},
{
name: "jim",
family: "smith",
job: "Devops"
}
];
const txt =
` <ul>
${jobs.map(job => `<li>${job.name} ${job.family} -> ${job.job}</li>`).join('')}
</ul>`
;
document.body.innerHTML = txt;
Be careful about the back Ticks (`)
This might help somebody. Maybe it's a bug in Node.
var arr = [ { name: 'a' }, { name: 'b' }, { name: 'c' } ];
var c = 0;
This doesn't work:
while (arr[c].name) { c++; } // TypeError: Cannot read property 'name' of undefined
But this works...
while (arr[c]) { c++; } // Inside the loop arr[c].name works as expected.
This works too...
while ((arr[c]) && (arr[c].name)) { c++; }
BUT simply reversing the order does not work. I'm guessing there's some kind of internal optimization here that breaks Node.
while ((arr[c].name) && (arr[c])) { c++; }
Error says the array is undefined, but it's not :-/ Node v11.15.0
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