How can I hash a string with SHA256 in JS?

Question

Description

I'm looking to hash a string locally with SHA256 in Javascript. I've been looking around thinking there would be some sort of official library or function, but all I found were loads of different projects, each with different scripts, and I'm not so sure scripts to trust (as I'm not an expert and definitely not qualified to evaluate them) or how to implement them. EDIT: I need the output in text, not hexes, sorry if I didn't explain that when posting the original question.

Code

Here's what I've tried so far:

async function sha256(message) {
  // encode as UTF-8
  const msgBuffer = new TextEncoder('utf-8').encode(message);

  // hash the message
  const hashBuffer = await crypto.subtle.digest('SHA-256', msgBuffer);

  // convert ArrayBuffer to Array
  const hashArray = Array.from(new Uint8Array(hashBuffer));

  // convert bytes to hex string
  const hashHex = hashArray.map(b => ('00' + b.toString(16)).slice(-2)).join('');
  console.log(hashHex);
  return hashHex;
}
sha256(passwordInput); 

Console Output:

Uncaught (in promise) TypeError: Cannot read property 'digest' of undefined

I'm new to javascript and I'm open to all suggestions, so yeah.

Update

Although most of your suggestions work, for those of you who are looking to use the Web Crypto API, the answer was on line #5. I needed to change crypto.subtle.digest to window.crypto.subtle.digest

Answer 1

Hellow there :D it's quite a function. If you are a scholar, you would like to check this article: https://www.movable-type.co.uk/scripts/sha256.html

Pure javascript:

var sha256 = function sha256(ascii) {
    function rightRotate(value, amount) {
        return (value>>>amount) | (value<<(32 - amount));
    };
    
    var mathPow = Math.pow;
    var maxWord = mathPow(2, 32);
    var lengthProperty = 'length'
    var i, j; // Used as a counter across the whole file
    var result = ''

    var words = [];
    var asciiBitLength = ascii[lengthProperty]*8;
    
    //* caching results is optional - remove/add slash from front of this line to toggle
    // Initial hash value: first 32 bits of the fractional parts of the square roots of the first 8 primes
    // (we actually calculate the first 64, but extra values are just ignored)
    var hash = sha256.h = sha256.h || [];
    // Round constants: first 32 bits of the fractional parts of the cube roots of the first 64 primes
    var k = sha256.k = sha256.k || [];
    var primeCounter = k[lengthProperty];
    /*/
    var hash = [], k = [];
    var primeCounter = 0;
    //*/

    var isComposite = {};
    for (var candidate = 2; primeCounter < 64; candidate++) {
        if (!isComposite[candidate]) {
            for (i = 0; i < 313; i += candidate) {
                isComposite[i] = candidate;
            }
            hash[primeCounter] = (mathPow(candidate, .5)*maxWord)|0;
            k[primeCounter++] = (mathPow(candidate, 1/3)*maxWord)|0;
        }
    }
    
    ascii += '\x80' // Append Ƈ' bit (plus zero padding)
    while (ascii[lengthProperty]%64 - 56) ascii += '\x00' // More zero padding
    for (i = 0; i < ascii[lengthProperty]; i++) {
        j = ascii.charCodeAt(i);
        if (j>>8) return; // ASCII check: only accept characters in range 0-255
        words[i>>2] |= j << ((3 - i)%4)*8;
    }
    words[words[lengthProperty]] = ((asciiBitLength/maxWord)|0);
    words[words[lengthProperty]] = (asciiBitLength)
    
    // process each chunk
    for (j = 0; j < words[lengthProperty];) {
        var w = words.slice(j, j += 16); // The message is expanded into 64 words as part of the iteration
        var oldHash = hash;
        // This is now the undefinedworking hash", often labelled as variables a...g
        // (we have to truncate as well, otherwise extra entries at the end accumulate
        hash = hash.slice(0, 8);
        
        for (i = 0; i < 64; i++) {
            var i2 = i + j;
            // Expand the message into 64 words
            // Used below if 
            var w15 = w[i - 15], w2 = w[i - 2];

            // Iterate
            var a = hash[0], e = hash[4];
            var temp1 = hash[7]
                + (rightRotate(e, 6) ^ rightRotate(e, 11) ^ rightRotate(e, 25)) // S1
                + ((e&hash[5])^((~e)&hash[6])) // ch
                + k[i]
                // Expand the message schedule if needed
                + (w[i] = (i < 16) ? w[i] : (
                        w[i - 16]
                        + (rightRotate(w15, 7) ^ rightRotate(w15, 18) ^ (w15>>>3)) // s0
                        + w[i - 7]
                        + (rightRotate(w2, 17) ^ rightRotate(w2, 19) ^ (w2>>>10)) // s1
                    )|0
                );
            // This is only used once, so *could* be moved below, but it only saves 4 bytes and makes things unreadble
            var temp2 = (rightRotate(a, 2) ^ rightRotate(a, 13) ^ rightRotate(a, 22)) // S0
                + ((a&hash[1])^(a&hash[2])^(hash[1]&hash[2])); // maj
            
            hash = [(temp1 + temp2)|0].concat(hash); // We don't bother trimming off the extra ones, they're harmless as long as we're truncating when we do the slice()
            hash[4] = (hash[4] + temp1)|0;
        }
        
        for (i = 0; i < 8; i++) {
            hash[i] = (hash[i] + oldHash[i])|0;
        }
    }
    
    for (i = 0; i < 8; i++) {
        for (j = 3; j + 1; j--) {
            var b = (hash[i]>>(j*8))&255;
            result += ((b < 16) ? 0 : '') + b.toString(16);
        }
    }
    return result;
};

Source: https://geraintluff.github.io/sha256/

Answer 2

2021 update - SHA256 is now included in current browsers

As you mention in your question, you don't need custom Crypto implementations to do this.

WebCrypto is supported in all current browsers. Use window.crypto.subtle.digest to make a SHA 256 hash.

const digest = await window.crypto.subtle.digest('SHA-256', data);

If you want something asynchronous, sha.js for example has 12.8 million downloads a month, and is actively maintained.

const digest = shajs('sha256').update(data).digest('hex')