Lists and keys
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What does .map() return? after iterate on array its return the new value.
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If I want to loop through an array and display each value in JSX, how do I do that in React? write array then using map to iterates through an array and call value then but every value in JSX.
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Each list item needs a unique key.
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What is the purpose of a key? Keys help React identify which items have changed, are added, or are removed.Source
The Spread Operator
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What is the spread operator? The spread operator is a useful and quick syntax for adding items to arrays, combining arrays or objects, and spreading an array out into a function’s arguments.
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List 4 things that the spread operator can do. Copying an array,Concatenating or combining arrays,Using Math functions,Using an array as arguments.
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Give an example of using the spread operator to combine two arrays. let arr1 = [a,b,c] let arr2 = [d,e,f] let arr3 = […arr1, …arr2] //[a,b,c,d,e,f]
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Give an example of using the spread operator to add a new item to an array. let arr1=[a,b,c] let arr2=[…arr1,d]//[a,b,c,d]
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Give an example of using the spread operator to combine two objects into one. let arr1=[a,b,c] let arr2=[d,e,f] let arr3=[…arr1,…arr2,g]//[a,b,c,d,e,f,g]
How to Pass Functions Between Components
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In the video, what is the first step that the developer does to pass functions between components? looping through the array genrating these objects,using array map method.
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In your own words, what does the increment function do? change the state.
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How can you pass a method from a parent component into a child component? calling parent by passing the state of it then call using the props in child.
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How does the child component invoke a method that was passed to it from a parent component? using state.