Catch Off By One Errors When Using Indexing
Off by one errors (sometimes called OBOE) crop up when you're trying to target a specific index of a string or array (to slice or access a segment), or when looping over the indices of them. JavaScript indexing starts at zero, not one, which means the last index is always one less than the length of the item.
JavaScript arrays are zero-indexed: the first element of an array is at index 0 , the second is at index 1 , and so on — and the last element is at the value of the array's length property minus 1.
What is the undefined in JavaScript? A variable that has not been assigned a value is of type undefined . A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value. A function returns undefined if a value was not returned.
How to fix undefined error in JavaScript?
2. Scenarios that create undefined
Tip 1: Favor const , otherwise use let , but say goodbye to var.
Tip 2: Increase cohesion.
Tip 3: Check the property existence.
Tip 4: Destructuring to access object properties.
Tip 5: Fill the object with default properties.
Bonus tip: nullish coalescing.
Tip 6: Use default parameter value.