Category: JavaScript Answers

Sometimes, we want to fix Cannot read property ‘push’ of undefined when combining arrays with JavaScript.

In this article, we’ll look at how to fix Cannot read property ‘push’ of undefined when combining arrays with JavaScript.

How to fix Cannot read property ‘push’ of undefined when combining arrays with JavaScript?

To fix Cannot read property ‘push’ of undefined when combining arrays with JavaScript, we should make sure we’re calling push on an array.

For instance, we write

const order = new Array();
order.push(a[n]);

to call order.push to append a new entry into the order array.

Conclusion

To fix Cannot read property ‘push’ of undefined when combining arrays with JavaScript, we should make sure we’re calling push on an array.

Sometimes, we want to change the key name in an array of objects with JavaScript.

In this article, we’ll look at how to change the key name in an array of objects with JavaScript.

How to change the key name in an array of objects with JavaScript?

To change the key name in an array of objects with JavaScript, we use the array map method.

For instance, we write

const arrayOfObj = [
  {
    key1: "value1",
    key2: "value2",
  },
  {
    key1: "value1",
    key2: "value2",
  },
];
const newArrayOfObj = arrayOfObj.map(({ key1: stroke, ...rest }) => ({
  stroke,
  ...rest,
}));

console.log(newArrayOfObj);

to call arrayOfObj.map with a function that destructures the object we’re iterating through.

Then we return a new object that has the stroke property and the rest object’s properties spread into the returned object.

rest is an object with properties other than key1.

We rename key1 to stroke when we’re destructuring.

Conclusion

To change the key name in an array of objects with JavaScript, we use the array map method.

Sometimes, we want to use a regex to remove letters and symbols except numbers with JavaScript.

In this article, we’ll look at how to use a regex to remove letters and symbols except numbers with JavaScript.

How to use a regex to remove letters and symbols except numbers with JavaScript?

To use a regex to remove letters and symbols except numbers with JavaScript, we can use the string replace method.

For instance, we write

const removedText = str.replace(/\D+/g, "");

to call str.replace with /\D+/g and an empty string to return a new string with the non-digit characters in str removed.

Conclusion

To use a regex to remove letters and symbols except numbers with JavaScript, we can use the string replace method.

Sometimes, we want to search an array for matching attribute with JavaScript.

In this article, we’ll look at how to search an array for matching attribute with JavaScript.

How to search an array for matching attribute with JavaScript?

To search an array for matching attribute with JavaScript, we use the array find method.

For instance, we write

const restaurants = [
  { restaurant: { name: "McDonald's", food: "burger" } },
  { restaurant: { name: "KFC", food: "chicken" } },
  { restaurant: { name: "Pizza Hut", food: "pizza" } },
];

const chickenRestaurant = restaurants.find((item) => {
  return item.restaurant.food === "chicken";
});

to call restaurants.find with a callback that returns the first object in restaurants that has the restaurant.food property equal to 'chicken'.

Conclusion

To search an array for matching attribute with JavaScript, we use the array find method.

Sometimes, we want to exclude one particular field from a collection in Mongoose and JavaScript.

In this article, we’ll look at how to exclude one particular field from a collection in Mongoose and JavaScript.

How to exclude one particular field from a collection in Mongoose and JavaScript?

To exclude one particular field from a collection in Mongoose and JavaScript, we call the select method.

For instance, we write

const products = await Product.find().select(["-image"]);

to call select with an array with "-image" to exclude the image field from the returned results.

Conclusion

To exclude one particular field from a collection in Mongoose and JavaScript, we call the select method.