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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Build a Quiz Challenge, Part 2

William Bok
William Bok
6,842 Points
Posted by William Bok
William Bok
6,842 Points

VM5944:13 Uncaught TypeError: Cannot read property '0' of undefined(…)

var userInput = ""; var numberOfCorrect = ""; var correctQuestions = []; var incorrectQuestions = []; var results = [ ["You got " + numberOfCorrect + "question(s) right."], ["You got these questions correct:"], [correctQuestions], ["You got these questions wrong:"], [incorrectQuestions] ];

var quiz = [ [ "What is 20 squared?" , "400" ], [ "What colour is the sky?" , "blue" ], [ "How many wheels on a bike?" , "2" ] ];

function answer( questions ) {

for ( i=0; i<questions.length; i+=1 ) { userInput = prompt ( questions [i][0] ); }

if ( userInput.toLowerCase() === questions [i][1] ) { numberOfCorrect+=1; correctQuestions[ questions [i][0] ]; } else { incorrectQuestions [ questions [i][0] ]; }

}

answer(quiz);

function print(message) { document.write (message); } print(results);

1 Answer

Benjamin Barslev Nielsen
Benjamin Barslev Nielsen
18,958 Points
Benjamin Barslev Nielsen
Benjamin Barslev Nielsen
18,958 Points

The problem is with the for loop:

for ( i=0; i<=questions.length; i+=1 ) { 
    userInput = prompt ( questions [i][0] ); 
}

questions[questions.length] is undefined, so you should change the <= to <, such that the code is:

for ( i=0; i<questions.length; i+=1 ) { 
    userInput = prompt ( questions [i][0] ); 
}
William Bok
William Bok
6,842 Points
William Bok
William Bok
6,842 Points

Thanks for the quick response! I've changed the sign but still getting the error VM70:45 Uncaught TypeError: Cannot read property '1' of undefined(…)

Benjamin Barslev Nielsen
Benjamin Barslev Nielsen
18,958 Points
Benjamin Barslev Nielsen
Benjamin Barslev Nielsen
18,958 Points

Ok, there is another problem, you do not use your userInput inside the loop: 

for ( i=0; i<questions.length; i+=1 ) { 
     userInput = prompt ( questions [i][0] ); 
}

if ( userInput.toLowerCase() === questions [i][1] ) { 
    numberOfCorrect+=1; correctQuestions[ questions [i][0] ]; 
} else { 
    incorrectQuestions [ questions [i][0] ]; }
}

The if-statement you have that checks the userinput is outside the loop, which means that it is first run, after all the iterations in the loop, i.e., when i = questions.length. Therefore you should put the if-statement inside the loop-body:

for ( i=0; i<questions.length; i+=1 ) { 
     userInput = prompt ( questions [i][0] ); 
     if ( userInput.toLowerCase() === questions [i][1] ) { 
        numberOfCorrect+=1; correctQuestions[ questions [i][0] ]; 
     } else { 
        incorrectQuestions [ questions [i][0] ];
     }
}

There is still a couple of problems with the code, but now the TypeError should be solved.