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140 lines
4.0 KiB
140 lines
4.0 KiB
/**
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* @prototype StepNumber
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* The class StepNumber is an iterator for Numbers. You provide a start and end
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* value, and a best step size. StepNumber itself rounds to fixed values and
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* a finds the step that best fits the provided step.
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*
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* If prettyStep is true, the step size is chosen as close as possible to the
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* provided step, but being a round value like 1, 2, 5, 10, 20, 50, ....
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*
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* Example usage:
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* var step = new StepNumber(0, 10, 2.5, true);
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* step.start();
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* while (!step.end()) {
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* alert(step.getCurrent());
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* step.next();
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* }
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*
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* Version: 1.0
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*
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* @param {Number} start The start value
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* @param {Number} end The end value
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* @param {Number} step Optional. Step size. Must be a positive value.
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* @param {boolean} prettyStep Optional. If true, the step size is rounded
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* To a pretty step size (like 1, 2, 5, 10, 20, 50, ...)
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*/
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function StepNumber(start, end, step, prettyStep) {
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// set default values
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this._start = 0;
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this._end = 0;
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this._step = 1;
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this.prettyStep = true;
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this.precision = 5;
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this._current = 0;
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this.setRange(start, end, step, prettyStep);
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};
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/**
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* Set a new range: start, end and step.
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*
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* @param {Number} start The start value
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* @param {Number} end The end value
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* @param {Number} step Optional. Step size. Must be a positive value.
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* @param {boolean} prettyStep Optional. If true, the step size is rounded
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* To a pretty step size (like 1, 2, 5, 10, 20, 50, ...)
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*/
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StepNumber.prototype.setRange = function(start, end, step, prettyStep) {
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this._start = start ? start : 0;
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this._end = end ? end : 0;
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this.setStep(step, prettyStep);
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};
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/**
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* Set a new step size
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* @param {Number} step New step size. Must be a positive value
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* @param {boolean} prettyStep Optional. If true, the provided step is rounded
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* to a pretty step size (like 1, 2, 5, 10, 20, 50, ...)
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*/
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StepNumber.prototype.setStep = function(step, prettyStep) {
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if (step === undefined || step <= 0)
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return;
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if (prettyStep !== undefined)
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this.prettyStep = prettyStep;
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if (this.prettyStep === true)
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this._step = StepNumber.calculatePrettyStep(step);
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else
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this._step = step;
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};
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/**
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* Calculate a nice step size, closest to the desired step size.
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* Returns a value in one of the ranges 1*10^n, 2*10^n, or 5*10^n, where n is an
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* integer Number. For example 1, 2, 5, 10, 20, 50, etc...
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* @param {Number} step Desired step size
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* @return {Number} Nice step size
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*/
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StepNumber.calculatePrettyStep = function (step) {
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var log10 = function (x) {return Math.log(x) / Math.LN10;};
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// try three steps (multiple of 1, 2, or 5
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var step1 = Math.pow(10, Math.round(log10(step))),
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step2 = 2 * Math.pow(10, Math.round(log10(step / 2))),
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step5 = 5 * Math.pow(10, Math.round(log10(step / 5)));
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// choose the best step (closest to minimum step)
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var prettyStep = step1;
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if (Math.abs(step2 - step) <= Math.abs(prettyStep - step)) prettyStep = step2;
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if (Math.abs(step5 - step) <= Math.abs(prettyStep - step)) prettyStep = step5;
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// for safety
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if (prettyStep <= 0) {
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prettyStep = 1;
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}
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return prettyStep;
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};
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/**
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* returns the current value of the step
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* @return {Number} current value
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*/
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StepNumber.prototype.getCurrent = function () {
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return parseFloat(this._current.toPrecision(this.precision));
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};
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/**
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* returns the current step size
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* @return {Number} current step size
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*/
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StepNumber.prototype.getStep = function () {
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return this._step;
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};
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/**
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* Set the current value to the largest value smaller than start, which
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* is a multiple of the step size
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*/
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StepNumber.prototype.start = function() {
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this._current = this._start - this._start % this._step;
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};
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/**
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* Do a step, add the step size to the current value
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*/
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StepNumber.prototype.next = function () {
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this._current += this._step;
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};
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/**
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* Returns true whether the end is reached
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* @return {boolean} True if the current value has passed the end value.
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*/
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StepNumber.prototype.end = function () {
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return (this._current > this._end);
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};
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module.exports = StepNumber;
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