writetome51 / error-if-index-not-valid-after-offset-was-added

Function triggers error if passed index is not valid, assuming an offset was recently added to it

errorIfIndexNotValidAfterOffsetWasAdded(
      index,
      arrayLength
): void

Triggers error if index is not valid, assuming an offset was recently added to it.
For example, if you're writing a getIndex() function that gives you the option of adding
an offset to modify the index it returns, errorIfIndexNotValidAfterOffsetWasAdded()
might come in handy. For more info, read the example below.

Example

function getIndexSlightlyOff(value, array, offset){
    let index = array.indexOf(value);
    index += offset;
    // Now check if index still valid:
    errorIfIndexNotValidAfterOffsetWasAdded(index, array.length);
    return index;
}

let arr = [1,2,3,4,5];
let index = getIndexSlightlyOff(5, arr, 1);
// Error: "After the offset was added to the index, the resulting 
// index was too high for this array"

let arr = [1,2,3,4,5];
let index = getIndexSlightlyOff(2, arr, -2);
// Error: "After the offset was added to the index, the resulting 
// index was a negative number. This is not allowed."

Installation

npm install error-if-index-not-valid-after-offset-was-added

Loading

// if using TypeScript:
import { errorIfIndexNotValidAfterOffsetWasAdded } 
    from 'error-if-index-not-valid-after-offset-was-added';
// if using ES5 JavaScript:
var errorIfIndexNotValidAfterOffsetWasAdded = 
    require('error-if-index-not-valid-after-offset-was-added')
    .errorIfIndexNotValidAfterOffsetWasAdded;

License

MIT