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thumbStyle

如何让 json 转为 style 样式字符串， 适用于小程序

'use strict';

/**
 * CSS properties which accept numbers but are not in units of "px".
 */
var isUnitlessNumber = {
    boxFlex: true,
    boxFlexGroup: true,
    columnCount: true,
    flex: true,
    flexGrow: true,
    flexPositive: true,
    flexShrink: true,
    flexNegative: true,
    fontWeight: true,
    lineClamp: true,
    lineHeight: true,
    opacity: true,
    order: true,
    orphans: true,
    widows: true,
    zIndex: true,
    zoom: true,

    // SVG-related properties
    fillOpacity: true,
    strokeDashoffset: true,
    strokeOpacity: true,
    strokeWidth: true
};

/**
 * @param {string} prefix vendor-specific prefix, eg: Webkit
 * @param {string} key style name, eg: transitionDuration
 * @return {string} style name prefixed with `prefix`, properly camelCased, eg:
 * WebkitTransitionDuration
 */
function prefixKey(prefix, key) {
    return prefix + key.charAt(0).toUpperCase() + key.substring(1);
}

/**
 * Support style names that may come passed in prefixed by adding permutations
 * of vendor prefixes.
 */
var prefixes = ['Webkit', 'ms', 'Moz', 'O'];

// Using Object.keys here, or else the vanilla for-in loop makes IE8 go into an
// infinite loop, because it iterates over the newly added props too.
Object.keys(isUnitlessNumber).forEach(function(prop) {
    prefixes.forEach(function(prefix) {
        isUnitlessNumber[prefixKey(prefix, prop)] = isUnitlessNumber[prop];
    });
});

var msPattern = /^ms-/;

var _uppercasePattern = /([A-Z])/g;

/**
 * Hyphenates a camelcased string, for example:
 *
 *   > hyphenate('backgroundColor')
 *   < "background-color"
 *
 * For CSS style names, use `hyphenateStyleName` instead which works properly
 * with all vendor prefixes, including `ms`.
 *
 * @param {string} string
 * @return {string}
 */
function hyphenate(string) {
    return string.replace(_uppercasePattern, '-$1').toLowerCase();
}

/**
 * Hyphenates a camelcased CSS property name, for example:
 *
 *   > hyphenateStyleName('backgroundColor')
 *   < "background-color"
 *   > hyphenateStyleName('MozTransition')
 *   < "-moz-transition"
 *   > hyphenateStyleName('msTransition')
 *   < "-ms-transition"
 *
 * As Modernizr suggests (http://modernizr.com/docs/#prefixed), an `ms` prefix
 * is converted to `-ms-`.
 *
 * @param {string} string
 * @return {string}
 */
function hyphenateStyleName(string) {
    return hyphenate(string).replace(msPattern, '-ms-');
}

var isArray = Array.isArray;
var keys = Object.keys;

var counter = 1;
// Follows syntax at https://developer.mozilla.org/en-US/docs/Web/CSS/content,
// including multiple space separated values.
var unquotedContentValueRegex = /^(normal|none|(\b(url\([^)]*\)|chapter_counter|attr\([^)]*\)|(no-)?(open|close)-quote|inherit)((\b\s*)|$|\s+))+)$/;

function buildRule(key, value) {
    if (!isUnitlessNumber[key] && typeof value === 'number') {
        value = '' + value + 'px';
    } else if (key === 'content' && !unquotedContentValueRegex.test(value)) {
        value = "'" + value.replace(/'/g, "\\'") + "'";
    }

    return hyphenateStyleName(key) + ': ' + value + ';  ';
}

function styleToCssString(rules) {
    var result = ''
    if (typeof rules === 'string') {
        return rules
    }
    if (!rules || keys(rules).length === 0) {
        return result;
    }
    var styleKeys = keys(rules);
    for (var j = 0, l = styleKeys.length; j < l; j++) {
        var styleKey = styleKeys[j];
        var value = rules[styleKey];

        if (isArray(value)) {
            for (var i = 0, len = value.length; i < len; i++) {
                result += buildRule(styleKey, value[i]);
            }
        } else {
            result += buildRule(styleKey, value);
        }
    }
    return result;
}

module.exports = styleToCssString;