gistfile1.js

var categories = [
	{
		id: 0,
		name: 'Shoes',
		imageUrl: 'alkfaekfja0-43i'
	},
	{
		id: 1,
		name: 'Clothing',
		imageUrl: 'someshit'
	},
	{
		id: 2,
		name: 'Facial Care',
		imageUrl: ''
	}
];

var products = [
	{
		name: 'Fancy Shoes',
		categories: [ 0, 1 ]
		imageUrl: ''
	},
	{
		name: 'Some Lipstick',
		categories: [ 2 ],
		imageUrl: ''
	}
];

function getCategory ( categoryName ) {
	for ( var i = 0; i < categories.length; i++ ) {
		if ( categories[ i ].categoryName === categoryName ) {
			return categories[ i ];
		}
	}
}

function getProductsByCategory ( categoryName ) {
	var category = getCategory( categoryName );

	var productsIWant = [];

	for ( var i = 0; i < products.length; i++ ) {
		for ( var j = 0; j < products[ i ].categories.length; j++ ) {
			if ( products[ i ].categories[ j ] === category.id ) {
				productsIWant.push( products );
			}
		}
	}

	return productsIWant;
}