The simplest way would be to generate two random numbers from 0-50 and add them together.

This gives a distribution biased towards 50, in the same way rolling two dice biases towards 7.

In fact, by using a larger number of "dice" (as @Falco suggests), you can make a closer approximation to a bell-curve:

function weightedRandom(max, numDice) {

    let num = 0;

    for (let i = 0; i < numDice; i++) {

        num += Math.random() * (max/numDice);

    }    

    return num;

}

JSFiddle: http://jsfiddle.net/797qhcza/1/