aaac7fed
 liuqimichale
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/**
* Module dependencies
*/
var balanced = require("balanced-match")
var reduceFunctionCall = require("reduce-function-call")
var mexp = require("math-expression-evaluator")
/**
* Constantes
*/
var MAX_STACK = 100 // should be enough for a single calc()...
var NESTED_CALC_RE = /(\+|\-|\*|\\|[^a-z]|)(\s*)(\()/g
/**
* Global variables
*/
var stack
/**
* Expose reduceCSSCalc plugin
*
* @type {Function}
*/
module.exports = reduceCSSCalc
/**
* Reduce CSS calc() in a string, whenever it's possible
*
* @param {String} value css input
*/
function reduceCSSCalc(value, decimalPrecision) {
stack = 0
decimalPrecision = Math.pow(10, decimalPrecision === undefined ? 5 : decimalPrecision)
// Allow calc() on multiple lines
value = value.replace(/\n+/g, " ")
/**
* Evaluates an expression
*
* @param {String} expression
* @returns {String}
*/
function evaluateExpression (expression, functionIdentifier, call) {
if (stack++ > MAX_STACK) {
stack = 0
throw new Error("Call stack overflow for " + call)
}
if (expression === "") {
throw new Error(functionIdentifier + "(): '" + call + "' must contain a non-whitespace string")
}
expression = evaluateNestedExpression(expression, call)
var units = getUnitsInExpression(expression)
// If the expression contains multiple units or CSS variables,
// then let the expression be (i.e. browser calc())
if (units.length > 1 || expression.indexOf("var(") > -1) {
return functionIdentifier + "(" + expression + ")"
}
var unit = units[0] || ""
if (unit === "%") {
// Convert percentages to numbers, to handle expressions like: 50% * 50% (will become: 25%):
// console.log(expression)
expression = expression.replace(/\b[0-9\.]+%/g, function(percent) {
return parseFloat(percent.slice(0, -1)) * 0.01
})
}
// Remove units in expression:
var toEvaluate = expression.replace(new RegExp(unit, "gi"), "")
var result
try {
result = mexp.eval(toEvaluate)
}
catch (e) {
return functionIdentifier + "(" + expression + ")"
}
// Transform back to a percentage result:
if (unit === "%") {
result *= 100
}
// adjust rounding shit
// (0.1 * 0.2 === 0.020000000000000004)
if (functionIdentifier.length || unit === "%") {
result = Math.round(result * decimalPrecision) / decimalPrecision
}
// Add unit
result += unit
return result
}
/**
* Evaluates nested expressions
*
* @param {String} expression
* @returns {String}
*/
function evaluateNestedExpression(expression, call) {
// Remove the calc part from nested expressions to ensure
// better browser compatibility
expression = expression.replace(/((?:\-[a-z]+\-)?calc)/g, "")
var evaluatedPart = ""
var nonEvaluatedPart = expression
var matches
while ((matches = NESTED_CALC_RE.exec(nonEvaluatedPart))) {
if (matches[0].index > 0) {
evaluatedPart += nonEvaluatedPart.substring(0, matches[0].index)
}
var balancedExpr = balanced("(", ")", nonEvaluatedPart.substring([0].index))
if (balancedExpr.body === "") {
throw new Error("'" + expression + "' must contain a non-whitespace string")
}
var evaluated = evaluateExpression(balancedExpr.body, "", call)
evaluatedPart += balancedExpr.pre + evaluated
nonEvaluatedPart = balancedExpr.post
}
return evaluatedPart + nonEvaluatedPart
}
return reduceFunctionCall(value, /((?:\-[a-z]+\-)?calc)\(/, evaluateExpression)
}
/**
* Checks what units are used in an expression
*
* @param {String} expression
* @returns {Array}
*/
function getUnitsInExpression(expression) {
var uniqueUnits = []
var uniqueLowerCaseUnits = []
var unitRegEx = /[\.0-9]([%a-z]+)/gi
var matches = unitRegEx.exec(expression)
while (matches) {
if (!matches || !matches[1]) {
continue
}
if (uniqueLowerCaseUnits.indexOf(matches[1].toLowerCase()) === -1) {
uniqueUnits.push(matches[1])
uniqueLowerCaseUnits.push(matches[1].toLowerCase())
}
matches = unitRegEx.exec(expression)
}
return uniqueUnits
}
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