The last challenge showed how the <code>map</code> method is used to dynamically render a number of elements based on user input. However, there was an important piece missing from that example. When you create an array of elements, each one needs a <code>key</code> attribute set to a unique value. React uses these keys to keep track of which items are added, changed, or removed. This helps make the re-rendering process more efficient when the list is modified in any way.<br><br><strong>Note:</strong> Keys only need to be unique between sibling elements, they don't need to be globally unique in your application.
The code editor has an array with some front end frameworks and a stateless functional component named <code>Frameworks()</code>. <code>Frameworks()</code> needs to map the array to an unordered list, much like in the last challenge. Finish writing the <code>map</code> callback to return an <code>li</code> element for each framework in the <code>frontEndFrameworks</code> array. This time, make sure to give each <code>li</code> a <code>key</code> attribute, set to a unique value. The <code>li</code> elements should also contain text from <code>frontEndFrameworks</code>.
Normally, you want to make the key something that uniquely identifies the element being rendered. As a last resort the array index may be used, but typically you should try to use a unique identification.
testString: assert(Enzyme.mount(React.createElement(Frameworks)).find('Frameworks').length === 1, 'The <code>Frameworks</code> component should exist and render to the page.');
testString: assert(Enzyme.mount(React.createElement(Frameworks)).find('h1').length === 1, '<code>Frameworks</code> should render an <code>h1</code> element.');
testString: assert(Enzyme.mount(React.createElement(Frameworks)).find('ul').length === 1, '<code>Frameworks</code> should render a <code>ul</code> element.');
testString: assert((() => { const ul = Enzyme.mount(React.createElement(Frameworks)).find('ul'); const keys = new Set([ ul.childAt(0).key(), ul.childAt(1).key(), ul.childAt(2).key(), ul.childAt(3).key(), ul.childAt(4).key(), ul.childAt(5).key(), ]); return keys.size === 6; })(), 'Each list item element should have a unique <code>key</code> attribute.');
- text: Each list item element should contain text from <code>frontEndFrameworks</code>.
testString: assert((() => {const li = Enzyme.mount(React.createElement(Frameworks)).find('ul').children(); return [...Array(5)].every((_, i) => frontEndFrameworks.includes(li.at(i).text()))})(), 'Each list item element should contain text from <code>frontEndFrameworks</code');