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JavaScript

Aaron Lipinski
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Aaron Lipinski
Full Stack JavaScript Techdegree Graduate 15,990 Points
Posted by Aaron Lipinski
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Aaron Lipinski
Full Stack JavaScript Techdegree Graduate 15,990 Points

Help getting Math.random() to not return the same value twice.

I currently have my function pulling a random quote from my array of quotes. I'd like to not repeat the quote when pulled. Im having trouble figuring out how to make this happen.

can achieve this which the current function I have made. Do I need to push quotes into a empty array then check with an if statement to compare is the quote already exists? 

function getRandomQuote(){
    randomNumber = Math.floor(Math.random() * quotes.length);
        return quotes[randomNumber];
}

This function is called later in another function.

   function printQuote(){
    randomQuote = getRandomQuote(quotes);
    htmlToPage = '<p class="quote">' + randomQuote.quote +'</p>';
    htmlToPage +='<p class="source">' + randomQuote.source;
    if(randomQuote.citation){
        htmlToPage += '<span class="citation">' + randomQuote.citation + '</span>';
    }
    if(randomQuote.year){ 
        htmlToPage += '<span class="year">' + randomQuote.year + '</span>';
    }
    if(randomQuote.category){
        htmlToPage += '<span class="category">' +  " " + randomQuote.catagory + '</p>';
    }
    htmlToPage += '</p>';
    random_bg_color();
    document.getElementById('quote-box').innerHTML = htmlToPage; 
}

Hope this makes sense.

2 Answers

Steven Parker
Steven Parker
230,274 Points
Steven Parker
Steven Parker
230,274 Points

An even better strategy might be to remove each quote as it is is used from the original array and store it in another one. Then, before picking one, check of the source array is depleted and restore it from the storage array if so. That guarantees that no quote will be shown twice until all have been used once.

If you care to search the previous questions, I'm pretty sure I've seen an example of this posted before (perhaps even by me!).

Aaron Lipinski
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Aaron Lipinski
Full Stack JavaScript Techdegree Graduate 15,990 Points
Aaron Lipinski
.a{fill-rule:evenodd;}techdegree seal-36
Aaron Lipinski
Full Stack JavaScript Techdegree Graduate 15,990 Points

After searching and tinkering I think I got it. Although full transparency, I did have to look at some example code to get it. 

function getRandomQuote(){
    pullQuote = Math.floor(Math.random() * quotes.length);
    spliceQuote = quotes.splice(pullQuote, 1)[0];
    usedQuote.push(spliceQuote);
    if(quotes.length == 0){
        quotes = usedQuote;
        usedQuote = [];
    }
    return spliceQuote;
}