The indexOf() method returns the position of a value in a string's first occurrence. If the value cannot be retrieved, the indexOf() method returns -1.
Reordering an item alters the index if the key is an index. As a result, the component state may become jumbled, and the old key may be used for a different component instance. React can't tell if an element was removed or merely the content was updated without a unique key.
indexOf returns the first index in the array where a specified element can be found, or -1 if it does not exist. So index is simply the counter's index in counters. You're making a comparison between an object (counter) and a number ( index ).
The indexOf() method is used for a single-dimensional array of primitive datatypes such as string, number, and so on.
When looking for an index value from an object element, the findIndex() method is used.
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Very helpful course in learning ReactJS
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VERY GOOD COURSE OF REACT JS
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I gave it 5 stars for their work. Topics are covered very well.but one thing which I would like to say to the teachers that you covered very good but try to cover more things and use less English words. Except this all things are best.
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This series is usefull for just starting and building confident. Go further and explore more about React JS
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