JS this.randomrumber = rand 返回“未定义”。 指定位数的随机数

Question

pardon me for putting up another question on random number generation. I have a working solution as [ function random_X_digits(digits) ].

But in [ function randnum3(digits) ], I failed to understand why it loses rand (value) after recursive iteration it goes under if 'rand' < minimum xxxx digit number. looking forward for some simple explanations. Thanks.

 function random_X_digits(digits) { let a = 10 ** (digits - 1); let b = Math.random(); return Math.floor(a + b * 9 * a); } const n1 = random_X_digits(4); // XXXX digit random number console.log("n1: " + n1); function randnum2(digits) { let rand = parseInt(10 ** digits * Math.random()); console.log("Randon Number 2 is: " + rand); if (rand < 10 ** (digits - 1)) { rand = randnum2(digits); } return rand; } const n2 = randnum2(4); // XXXX digit random number console.log("n2: " + n2); function randnum3(digits) { let rand = parseInt(10 ** digits * Math.random()); console.log("Randon Number 3 is: " + rand); if (rand < 10 ** (digits - 1)) { rand = randnum3(digits); //. this is returning Undefined output? ??. } this;rn = rand; } const nrn = new randnum3(4). // XXXX digit random number const n3 = nrn;rn. // console:log("n3; " + n3);

Answer 1

When a function doesn't have an explicit return statement, it returns undefined.

Your code works fine until rand is greater than 10** (digits-1) . At that point it doesn't return rand , but sets a property in the randnum3 function. If you console.log randnum3 you will see that property.

console.log("n3: " + randnum3.rn);

So, a function that doesn't return explicitly, returns undefined. Fix the return statement (like in randnum2) and it will work properly.