Alternative to array.includes() in google apps script?

Question

I'm using range.getValues() to load an array in Google Apps Script.

var array = SpreadsheetApp.getActive().getActivesheet().getRange('E10:E30').getValues();
> array = [["val1"],["val2"],["val3"],["val4"]]

I then want to loop through a separate list to see whether its elements exist in the array, using array.prototype.includes():

if(array.includes("val4")) {doSomething;}

Using array.prototype.includes() like this does not work for two reasons: 1) since each element in array is an array in itself and 2) because the method isn't available in Google Apps Script:

TypeError: Cannot find function includes in object

Then wanted to use array.prototype.flat() to solve 1) but it seems it isn't available in Google Apps Script either. I get the following error:

TypeError: Cannot find function flat in object

This is something I could do using brute force, but surely there's a neat way of doing it?

Answer 1

EDIT(2019-04-07): Please be advised. With the expected V8 upgrade (ECMAScript 2017) for App Script, the language will natively support Array.prototype.includes and many other modern Javascript features in the near future.

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The simplest solution for array.prototype.includes is to use the following polyfill from MDN in your apps script project. Just create a script file and paste the following code - the code/polyfill will add the function directly to the Array prototype object:

// https://tc39.github.io/ecma262/#sec-array.prototype.includes
if (!Array.prototype.includes) {
  Object.defineProperty(Array.prototype, 'includes', {
    value: function(searchElement, fromIndex) {

      if (this == null) {
        throw new TypeError('"this" is null or not defined');
      }

      // 1. Let O be ? ToObject(this value).
      var o = Object(this);

      // 2. Let len be ? ToLength(? Get(O, "length")).
      var len = o.length >>> 0;

      // 3. If len is 0, return false.
      if (len === 0) {
        return false;
      }

      // 4. Let n be ? ToInteger(fromIndex).
      //    (If fromIndex is undefined, this step produces the value 0.)
      var n = fromIndex | 0;

      // 5. If n ≥ 0, then
      //  a. Let k be n.
      // 6. Else n < 0,
      //  a. Let k be len + n.
      //  b. If k < 0, let k be 0.
      var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);

      function sameValueZero(x, y) {
        return x === y || (typeof x === 'number' && typeof y === 'number' && isNaN(x) && isNaN(y));
      }

      // 7. Repeat, while k < len
      while (k < len) {
        // a. Let elementK be the result of ? Get(O, ! ToString(k)).
        // b. If SameValueZero(searchElement, elementK) is true, return true.
        if (sameValueZero(o[k], searchElement)) {
          return true;
        }
        // c. Increase k by 1. 
        k++;
      }

      // 8. Return false
      return false;
    }
  });
}

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For array.prototype.flat the MDN site also provides alternative solutions. One of which leverages array.prototype.reduce and array.prototype.concat:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat#Alternative