'hello world hello'.indexOf('o', 99) returns -1 - because 99 is greater than the length of hello world hello, which causes the method to not search the string at all.
'hello world hello'.indexOf('world', 12) returns -1 - because, while it's true the substring world occurs at index 6, that position is not greater than or equal to 12. 'hello world hello'.indexOf('o', -5) returns 4 - because it causes the method to behave as if the second argument were 0, and the first occurrence of o at a position greater or equal to 0 is at position 4. If position is less than zero, the method behaves as it would if position were 0. If position is greater than the length of the calling string, the method doesn't search the calling string at all. Consider this list with names: let names 'vera', 'chuck', 'dave' Here’s the code where two items match the condition. This means that it behaves like a FirstOrUndefined function. The method returns the index of the first occurrence of the specified substring at a position greater than or equal to position, which defaults to 0. The javascript find function returns either The first item that satisfies the condition or undefined. 
All values are coerced to strings, so omitting it or passing undefined causes indexOf() to search for the string "undefined", which is rarely what you want. Object.prototype._lookupSetter_() Deprecated.Object.prototype._lookupGetter_() Deprecated.Object.prototype._defineSetter_() Deprecated.Object.prototype._defineGetter_() Deprecated.
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