Category: JavaScript Answers

Sometimes, we want to sum elements at the same index in array of arrays into a single array with JavaScript.

In this article, we’ll look at how to sum elements at the same index in array of arrays into a single array with JavaScript.

How to sum elements at the same index in array of arrays into a single array with JavaScript?

To sum elements at the same index in array of arrays into a single array with JavaScript, we can use some array methods.

For instance, we write:

const arr = [
  [0, 1, 3],
  [2, 4, 6],
  [5, 5, 7],
  [10, 0, 3]
]
const [first] = arr
const sums = first.map((_, i) => {
  return arr.map(a => a[i]).reduce((a, b) => a + b, 0)
})
console.log(sums)

We get the first nested array from arr with destructuring and assign it to first.

Next, we call first.map with a callback that returns the items of each entry with the given index of each nested array.

Then we call reduce with a callback to sum all the entries together.

Therefore, sums is [17, 10, 19].

Conclusion

To sum elements at the same index in array of arrays into a single array with JavaScript, we can use some array methods.

Sometimes, we want to use an array as object keys in JavaScript.

In this article, we’ll look at how to use an array as object keys in JavaScript.

How to use an array as object keys in JavaScript?

To use an array as object keys in JavaScript, we can convert the array to a string.

For instance, we write:

const key = [1, 2, 3]
const obj = {
  [JSON.stringify(key)]: 'foo'
}
console.log(obj[JSON.stringify(key)])

to create the key array.

Then we convert it to a string with JSON.stringify so we can use it as a property key.

And we set the property’s value 'foo'.

Then we can access the value with obj[JSON.stringify(key)].

Therefore, the console log should log 'foo'.

Conclusion

To use an array as object keys in JavaScript, we can convert the array to a string.

Sometimes, we want to get pixel color from an image with JavaScript.

In this article, we’ll look at how to get pixel color from an image with JavaScript.

How to get pixel color from an image with JavaScript?

To get pixel color from an image with JavaScript, we can put the image in the canvas.

For instance, we write:

const myImg = new Image();
myImg.crossOrigin = "Anonymous";
myImg.onload = () => {
  const context = document.createElement('canvas').getContext('2d');
  context.drawImage(myImg, 0, 0);
  const {
    data
  } = context.getImageData(10, 10, 1, 1);
  console.log(data)
}
myImg.src = 'https://picsum.photos/200/300';

In myImg.onload we get the pixel data from the canvas by creating a canvas element with createElement.

Then we get the context with getContext.

Next, we call drawImage to draw the image.

And then we call getImageData with the x, y coordinates of the pixel to get as the first 2 arguments.

As a result, we see that data is a Uint8ClampedArray.

Conclusion

To get pixel color from an image with JavaScript, we can put the image in the canvas.

Sometimes, we want to convert a JavaScript date to SQL date object.

In this article, we’ll look at how to convert a JavaScript date to SQL date object.

How to convert a JavaScript date to SQL date object?

To convert a JavaScript date to SQL date object, we can use the JavaScript date’s toLocaleString method.

For instance, we write:

const date = (new Date(2022, 1, 1)).toLocaleString("en-US")
console.log(date)

to call toLocaleString with 'en-US' to convert return a date string formatted for the US English locale.

Therefore, date is '2/1/2022, 12:00:00 AM'.

Conclusion

To convert a JavaScript date to SQL date object, we can use the JavaScript date’s toLocaleString method.

Sometimes, we want to efficiently compare two integer arrays and find the items in both arrays with JavaScript.

In this article, we’ll look at how to efficiently compare two integer arrays and find the items in both arrays with JavaScript.

How to efficiently compare two integer arrays and find the items in both arrays with JavaScript?

To efficiently compare two integer arrays and find the items in both arrays with JavaScript, we can use some JavaScript array methods.

For instance, we write:

const a1 = [15, 551, 25, 910, 11]
const a2 = [25, 11, 785, 880, 15]
const inBoth = a1.filter(a => a2.includes(a))
console.log(inBoth)

to call a1.filter with a callback that checks if a1 array entry a is in a2 with a2.includes.

Therefore, inBoth is [15, 25, 11].

Conclusion

To efficiently compare two integer arrays and find the items in both arrays with JavaScript, we can use some JavaScript array methods.