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({value: 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({value: 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 val
• .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']

cjs([1,2,3]) and cjs({x: 1, y: 2}) are shorthand for cjs.array({value: [1,2,3]}) and cjs.map({value: {x: 1, y: 2}}).

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