Javascript: Round by 100 [duplicate]

问题

I'm trying to round a number the 100.

Example:

1340 should become 1400
1301 should become 1400

and

298 should become 300
200 should stay   200

I know about Math.round but it doesn't round to the 100.

How can I do that ?

回答1:

Try this...

function roundUp(value) {
    return (~~((value + 99) / 100) * 100);
}

That will round up to the next hundred - 101 will return 200.

jsFiddle example - http://jsfiddle.net/johncmolyneux/r8ryd/

Open your console to see the results.

回答2:

Original Answer

Use the Math.ceil function, such as:

var result = 100 * Math.ceil(value / 100);

Generalised Version

This function can be generalised as follows:

Number.prototype.roundToNearest = function (multiple, roundingFunction) {
    // Use normal rounding by default
    roundingFunction = roundingFunction || Math.round;

    return roundingFunction(this / multiple) * multiple;
}

Then you can use this function as follows:

var value1 = 8.5;
var value2 = 0.1;

console.log(value1.roundToNearest(5));              // Returns 10
console.log(value1.roundToNearest(5, Math.floor));  // Returns 5
console.log(value2.roundToNearest(2, Math.ceil));   // Returns 2

Or with a custom rounding function (such as banker's rounding):

var value1 = 2.5;
var value2 = 7.5;

var bankersRounding = function (value) {
    var intVal   = Math.floor(value);
    var floatVal = value % 1;

    if (floatVal !== 0.5) {
        return Math.round(value);
    } else {
        if (intVal % 2 == 0) {
            return intVal;
        } else {
            return intVal + 1;
        }
    }
}

console.log(value1.roundToNearest(5, bankersRounding)); // Returns 0
console.log(value2.roundToNearest(5, bankersRounding)); // Returns 10

An example of the code running is available here.

来源：https://stackoverflow.com/questions/17405899/javascript-round-by-100

标签

javascript

math

numbers

rounding