Group code and individual finish for testing

.gitignore

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+node_modules

inventory.js

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+function calculateDiscount(price, discountRate) {
+    if (typeof price !== 'number' || typeof discountRate !== 'number') { return `Price and Discount must be a number.`;} //When price or discountRate is not a number.
+    if (discountRate < 0 || discountRate > 1) { return `Discount must be a decimal value between 0 and 1.`;} //For discounts of less than 0 or greater than 100%
+    if (price <= 0) {return `Price must be a positive number.`;}
+    // TODO: Implement logic
+    return price * (1 - discountRate); //calculates discounted price
+}
+
+
+
+function filterProducts(products, callback) {
+    if (!Array.isArray(products) || typeof callback !== 'function') {return `Please use a valid array and filter`;}
+    else {return products.filter(callback);}
+}
+
+function sortInventory(inventory, key) {
+    if (!Array.isArray(inventory) || typeof key !== 'string') { return []; }
+    // TODO: Implement sorting logic
+    const sorted = [...inventory];
+    return sorted.sort((a, b) => {
+        if (a.hasOwnProperty(key) && b.hasOwnProperty(key)) {
+            const aKey = a[key];
+            const bKey = b[key];
+            if (typeof aKey === 'number' && typeof bKey === 'number') {
+                return aKey - bKey;
+            }  else if (typeof aKey === 'string' && typeof bKey === 'string' ) {
+                return aKey.localeCompare(bKey);
+            } return inventory;
+        } else {return inventory;}
+    })
+}
+
+module.exports = {
+    calculateDiscount,
+    filterProducts,
+    sortInventory
+};