tscope.js

Functional lenses in JavaScript

Basics

Tscope.attr('field') Object attribute accessor. Tscope.at(index) Array element accessor. lens.then(otherLens, ...) Lens composition can take many arguments. lens.traversal([filter]) Returns traversal, optionally filtered.

Regular lenses

Throw TypeError unless element has been found

var data = { array: [1, 2, 3] };
var firstOfSome = Tscope.attr('array').at(0);

// Getter
firstOfSome(data); //=> 1
firstOfSome.get(data); //=> 1

// Setter
firstOfSome(data, 10); //=> { array: [10, 2, 3] }
firstOfSome.set(data, 10); //=> { array: [10, 2, 3] }

// Modifier
var incr = function(x){ return x + 1 };
firstOfSome.mod(data, incr); //=> { array: [2, 2, 3] }

Partial lenses

Skip missing element

var data = { array: [1, 2, 3] };
var firstOfMissing = Tscope.partialAttr('missing').partialAt(0);

// Getter returns undefined
firstOfMissing(data); //=> undefined
firstOfMissing.get(data); //=> undefined

// Setter returns data unchanged
firstOfMissing(data, 10); //=> { array: [1, 2, 3] }
firstOfMissing.set(data, 10); //=> { array: [1, 2, 3] }

// Modifier returns data unchanged
var incr = function(x){ return x + 1 };
firstOfMissing.mod(data, incr); //=> { array: [1, 2, 3] }

Traversals

Traversals make working with series of data easy:

var data = {array: [{x: 0, y:9}, {x: 1, y: 8}, {x: 2, y: 7}]};
var traversal = Tscope.attr('array').traversal().attr('x');

traversal.get(data); //=> [0, 1, 2]
traversal.mod(data, incr) //=> {array: [{x: 1, y:9}, {x: 2, y: 8}, {x: 3, y: 7}]}
traversal.set(data, 6) //=> {array: [{x: 6, y:9}, {x: 6, y: 8}, {x: 6, y: 7}]}

// Nested traversals
var data = {users: [{id: 1, friends: ['Alice', 'Bob']}, {id: 2, friends: ['Sam']}]};
var traversal = Tscope.attr('users').traversal().attr('friends').traversal()

traversal.get(data)
//=> [['Alice', 'Bob'], ['Sam']]
traversal.mod(data, function (s) { return s.toUpperCase() })
//=> {users: [{id: 1, friends: ['ALICE', 'BOB']}, {id: 2, friends: ['SAM']}]};

Filtered traversals

Array elements can be traversed by calling .traversal([predicate]) on a lens that references an array. You can pass predicate in traversal to filter elements of an array or chain .traversal()).filter(predicate) function. Several .filter() functions can be chained one after another.

var data = {array: [{x: 0, y:9}, {x: 1, y: 8}, {x: 2, y: 7}]};
var x_gt_1 = function (el) { return el.x > 1; }
var traversal = Tscope.attr('array').traversal(x_gt_1).attr('x');
// Same as:
Tscope.attr('array').traversal().filter(x_gt_1).attr('x');

traversal.get(data); //=> [2]
traversal.mod(data, incr) //=> {array: [{x: 0, y:9}, {x: 1, y: 8}, {x: 3, y: 7}]}
traversal.set(data, 6) //=> {array: [{x: 0, y:9}, {x: 0, y: 8}, {x: 6, y: 7}]}

// Nested traversals
var data = {users: [{id: 1, friends: ['Alice', 'Bob']}, {id: 2, friends: ['Sam']}]};
var friendly = function (user) { return user.friends.length == 2; }
var threeLetter = function (s) { return s.length == 3; }
var traversal = Tscope.attr('users').traversal(friendly)
                      .attr('friends').traversal(threeLetter);

traversal.get(data)
//=> [['Bob']]
traversal.mod(data, function (s) { return s.toUpperCase() })
//=> {users: [{id: 1, friends: ['Alice', 'BOB']}, {id: 2, friends: ['Sam']}]};

Cursors

Tscope also provides cursors which are lenses enclosed over data or root accessors. Cursors a handy self-contained object to pass around. Cursors can be composed and traversed as regular lenses.

var data = {some: deep: 1};
var full = Tscope.dataCursor(data);
var deepLens = Tscope.attr('some').attr('deep');
var cursor = full.then(deepLens);

// Access
cursor() //=> 1
cursor.get() //=> 1

// Modify
cursor(42)
cursor.set(42)
cursor() //=> 42
full() //=> {some: deep: 42}
// All data are handled as immutable so original data is still:
data   //=> {some: deep: 1}

Cursor can notify about each change via callback:

var full = Tscope.dataCursor(data, function (newState, oldState) {
    // ... deal with it
})

This way it can be used with react.js. Inside a component:

var that = this;
var full = Tscope.dataCursor(this.state, function (state) {
  that.setState(state);
});
var childCursor = full.attr('child') // ... and pass it to a child component

Outside of a root component:

var root = <Root ... />;
Tscope.dataCursor({/** Initial data **/}, function (state) {
  root.setProps(state);
});
React.renderComponent(root, ...);