javascript Date.toISOString() return difference date value

I'm confusing about the javascript Date.toISOString() function which shown as below example, how come date value of x in ISO format become January?

const date = new Date();
const x = (new Date(date.getFullYear(), date.getMonth() , 1));

console.log(date); \\Tue Feb 04 2020 11:11:12 GMT+0800 (Malaysia Time)
console.log(x); \\Sat Feb 01 2020 00:00:00 GMT+0800 (Malaysia Time)

console.log(date.toISOString()); \\2020-02-04T03:11:12.330Z
console.log(x.toISOString()); \\2020-01-31T16:00:00.000Z