JavaScript: Calculate the nth root of a number

问题:

I'm trying to get the nth root of a number using JavaScript, but I don't see a way to do it using the built in Math object. Am I overlooking something?
If not...

Is there a math library I can use that has this functionality?
If not...

What's the best algorithm to do this myself?

回答1:

Can you use something like this?

Math.pow(n, 1/root); 

eg.

Math.pow(25, 1/2) == 5 

回答2:

The nth root of x is the same as x to the power of 1/n. You can simply use Math.pow:

var original = 1000; var fourthRoot = Math.pow(original, 1/4); original == Math.pow(fourthRoot, 4); // (ignoring floating-point error) 

回答3:

Use Math.pow()

Note that it does not handle negative nicely - here is a discussion and some code that does

http://cwestblog.com/2011/05/06/cube-root-an-beyond/

function nthroot(x, n) {   try {     var negate = n % 2 == 1 && x  0 == n > 0))       return negate ? -possible : possible;   } catch(e){} } 

回答4:

The n-th root of x is a number r such that r to the power of 1/n is x.

In real numbers, there are some subcases:

• There are two solutions (same value with opposite sign) when x is positive and r is even.
• There is one positive solution when x is positive and r is odd.
• There is one negative solution when x is negative and r is odd.
• There is no solution when x is negative and r is even.

Since Math.pow doesn't like a negative base with a non-integer exponent, you can use

function nthRoot(x, n) {   if(x 

Examples:

nthRoot(+4, 2); // 2 (the positive is chosen, but -2 is a solution too) nthRoot(+8, 3); // 2 (this is the only solution) nthRoot(-8, 3); // -2 (this is the only solution) nthRoot(-4, 2); // NaN (there is no solution) 

回答5:

You could use

Math.nthroot = function(x,n) {     //if x is negative function returns NaN     return this.exp((1/n)*this.log(x)); } //call using Math.nthroot(); 

回答6:

For the special cases of square and cubic root, it's best to use the native functions Math.sqrt and Math.cbrt respectively.

As of ES7, the exponentiation operator ** can be used to calculate the nth root as the ¹/_nth power of a non-negative base:

let root1 = Math.PI ** (1 / 3); // cube root of π  let root2 = 81 ** 0.25;         // 4th root of 81 

This doesn't work with negative bases, though.

let root3 = (-32) ** 5;         // NaN 

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