stackConstructorAttempt.js

import checkIfArray from './checkIfArray';

function checkIfString(x) {
    x.forEach(function(el) {
        if (typeof el !== 'string') {
            throw new Error('Array can only contain strings');
        }
    });
}

var StackConstructor = {
    init: function(delimiter = '||', input = '') {
        this.input = input;
		this.delimiter = delimiter;

		if (typeof input !== 'string' && !Array.isArray(input)) {
			throw new Error('Please enter a string or an array');
		}

		if(Array.isArray(input)) {
            checkIfString(input);
			this.input = input.join("||");
		}

		while(this.input.indexOf(this.delimiter) !== -1) {
			this.input = this.input.replace(this.delimiter, "[*-delimiter-*]");
		}
    },
    push: function(newString) {
        if (typeof newString !== 'string' && !Array.isArray(newString)) {
			throw new Error('Please enter a string or an array');
		}

		if(Array.isArray(newString)) {
            checkIfString(input);
			newString = newString.join("||");
		}

		while(newString.indexOf(this.delimiter) !== -1) {
			newString = newString.replace(this.delimiter, "[*-delimiter-*]");
		}

		this.input = this.input ? this.input + this.delimiter + newString : newString;
    },
    pop: function() {
        const LAST_INDEX = this.input.lastIndexOf(this.delimiter);

		if(!this.input) {
			throw new Error('Cannot execute push as current string is empty');
		}

		this.input = (LAST_INDEX !== -1) ? this.input.substring(0, LAST_INDEX) : '';
    },
    concat: function(newString) {
        if (typeof newString !== 'string') {
			throw new Error('Please enter a string');
		}

		return this.input ? this.input + this.delimiter + newString : newString;
    },
    indexesOf(n) {
        let indexesString = '';
		for(let i = 0; i < this.input.length; i++) {
			if(n === this.input[i]) {
				indexesString += i + ', ';
			}
		}

		let lastIndexofComma = indexesString.lastIndexOf(',');
		 return indexesString.substring(0, lastIndexofComma);
    }
}

// To use:
// var stackConstructorExample = Object.create(StackConstructor);
// stackConstructorExample.init("||", "example test case");