binary-search-promises

Javascript library to do binary search using promises. This allows for asynchronous comparison functions.

Usage

Install

npm install binary-search-promises

Arguments

function binarySearch(haystack, needle, compare, low, high)

• haystack - A sorted array.
• needle - The element to find in haystack.
• compare - A comparison function, with a twist. Instead of returning a result directly, it must return a Promise that will resolve to the comparison result. (The comparison algorithm should be the same as the one used to sort.)
• low - Optional lower bound of the haystack to consider. You probably don't need to use this.
• high - Optional upper bound of the haystack to consider. You probably don't need to use this.

compare is optional if dealing with numbers or strings.

If, for some reason, you want to use a synchronous comparison function, you can wrap it with binarySearch.wrapComparator().

Return

The function returns an array of two values:

• The first value indicates whether the needle was found in the haystack.
• The second value is the position of needle in haystack, if it was found. If it was not found, then it is the position where it should be inserted to maintain the sorting order.

Example

let binarySearch = require('binary-search-promises');

let haystack = [1,2,3,4,5,6,7,8,9];
let needle = 4;

binarySearch(haystack, needle, function(a, b) {
    let req = new Request(`/secret-comparison-algorithm/${a}/{$b}/`);
    fetch(req).then(function(response) {
        // For this example, the response comes back as one of -1, 0, or 1 as plain text.
        // text() returns a Promise that resolves to that text.
        return response.text();
    }).catch(function(reason) {
        return Promise.reject(reason);
    });
}).then(function(resolution) {
    let [found, position] = resolution;
    if (found) {
        console.log(`${needle} is at ${position}`);
    } else {
        console.log(`${needle} should be inserted at ${position}`);
    }
}).catch(function(reason) {
    console.error(reason);
});

Okay, that's a silly example. You're probably not going to be doing asynchronous comparisons on numbers.