What is the error in the program?

Pl notice this program code.I don’t obtain result.It is effective only till getting the age.When i tried your JSlint to try it states that ‘yearsLeft’ must be used before it can be defined.Where is a error Pl describe.Iam quite new for you to JS however.
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this.yearsToRetire = yearsLeft;

This doesn’t happen know just what exactly ‘yearsLeft’ will be, you didn’t defined the item as something.