Array & Map Constraints

So far, all of the constraint variables we have discussed have been simple objects (constructed using cjs.constraint(). However, constraint variables can also be arrays or objects (maps).

####Arrays cjs.array(arr) creates an Array constraint, which adds a constraint wrapper to all of the standard Array.prototype methods, including .pop(), .push(), etc.

It also includes the special methods:

• .length() to get the array's length
• .item(index) to get the item at index
• .item(index, val) to set the item at index to val
• .itemConstraint(index) to create a constraint whose value is always the array's value at index
• .toArray() converts this array to a JavaScript array

Example:

var arr = cjs.array({
              value: [1,2,3]
          });
arr.push(4);
arr.length(); // 4
arr.toArray(); // [1,2,3,4]

####Maps cjs.map(obj) creates a Map constraint, which adds a constraint wrapper to a standard object with key/value pairs. It contains a number of methods, including:

• .clear() to clear every key/value pair
• .keys() to fetch an array of keys
• .values() to fetch an array of values
• .forEach(callback) to loop through every key/value pair
• .has(key) to check if key is a key in the object
• .item(key) to get the value associated with key key
• .item(key, val) to set the value associated with key key to value
• .remove(key) to unset the value for key key
• .size() to get the number of entries
• .toObject() to convert the map to a JavaScript object

Example:

var m = cjs.map({
            value: {x: 1, y: 2}
        });
m.item('x'); // 1
m.item('z', 3);
m.keys(); // ['x','y','z']

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