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@jehugaleahsa
Created February 10, 2012 20:46
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Handle Optional Parameters with Default Values in JavaScript
function assignArguments(values, expression) {
// determine how many arguments are needed for each parameter
// grab all of the defaults, too
var needed = 1;
var argsNeeded = {};
var defaults = {};
var queue = [expression];
for (var queueIndex = 0; queueIndex < queue.length; ++queueIndex) {
var node = queue[queueIndex];
if (typeof node === 'string') {
// the node is a required parameter
argsNeeded[node] = needed;
++needed;
} else if (node instanceof Array) {
// the node is a list of parameters
for (var index = 0; index !== node.length; ++index) {
queue.push(node[index]);
}
} else {
// the node is a list of optional parameters with defaults
// make sure there isn't more than one parameter
var count = 0;
for (var key in node) {
if (node.hasOwnProperty(key)) {
if (count !== 0) {
throw new Error('A default parameter list had more than one value.');
}
defaults[key] = node[key];
queue.push(key);
++count;
}
}
}
}
// determine the order that the parameters appear
var parameters = [];
var stack = [expression];
while (stack.length > 0) {
var node = stack.pop();
if (typeof node === 'string') {
// the node is a required parameter
parameters.push(node);
} else if (node instanceof Array) {
// the node is a list of parameters
var index = node.length;
while (index !== 0) {
--index;
stack.push(node[index]);
}
} else {
// the node is an optional parameter with defaults
// we'll check for multiple parameters
var count = 0;
for (var key in node) {
if (node.hasOwnProperty(key)) {
if (count > 0) {
throw new Error('A default parameter list had more than one value.');
}
stack.push(key);
++count;
}
}
}
}
var result = {};
var valueIndex = 0;
for (var index = 0; index !== parameters.length; ++index) {
var parameter = parameters[index];
var needed = argsNeeded[parameter];
if (needed > values.length) {
if (parameter in defaults) {
result[parameter] = defaults[parameter];
}
} else {
result[parameter] = values[valueIndex];
++valueIndex;
}
}
return result;
}
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