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6: Advanced Types - Coggle Diagram

- - - - you can't call string functions on it
      - unless you cast it
        
        const result = add('Max', ' Schwarz') as string; result.split(' ');
- - - - except
        
        if the property is null or undefined
        
        the expression short-circuits
        
        with a return value of undefined
      - .
- - - - when its left-hand side operand is null or undefined
- - - - different messages
      - for different input fields
    - - the value is the error message
      - but we don't know in advance
        
        the exact identifiers we will use
        
        because we can't predict which fields will generate errors
    - - syntax
        
        square brackets
        
        where the property name would normally be
        
        a name of your choice
        
        can be anything
        
        colon
        
        the type that the property will have
        
        can be
        
        string
        
        number
        
        symbol
        
        tells TypeScript
        
        I don't know the property name
        
        or how many properties there will be
        
        but each property will have a name that is a string
        
        and its value will be a string
      - example object
        
        const errorBag: ErrorContainer = { email: 'Not a valid email!', username: 'Must start with a capital character!' };
        
        this would work :!:
        
        const errorBag: ErrorContainer = { 1: 'Not a valid email!', 2: 'Must start with a capital character!' };
        
        because numbers can be converted to strings implicitly
        
        but you couldn't do the reverse