watch

Receive notification when a fact is added or removed from query results. The notification function will initially recieve all matching facts. It will then subsequently receive new facts as they are created.

watch<T, U, V>(
    start: T,
    preposition: Preposition<T, U>,
    resultAdded: (result: U) => V,
    resultRemoved: (model: V) => void
): Watch<U, V>;

Parameters

start - A fact from which to begin the query
preposition - A template function passed into j.for
resultAdded - A function that is called when a fact is added
resultRemoved (optional) - A function that is called when a fact is removed

Returns

A Watch object that can be used to nest new watches or stop watching

Examples

Watch for new facts. Display them to the user as they arrive.

function displayMessage(m) {
    // Update the user interface
}

function messagesInChannel(c) {
    return j.match({
        type: 'Chat.Message',
        channel: c
    });
}

j.watch(channel, j.for(messagesInChannel), displayMessage);

Remove facts that no longer match the query. This will occur if the template function has a condition that later becomes false. The resultAdded function must return a value. This value will be pased to resultRemoved when the condition changes.

function displayMessage(m) {
    // Update the user interface
    return domElement;
}

function removeMessage(domElement) {
    // Remove the message from the user interface
}

function messagesInChannel(c) {
    return j.match({
        type: 'Chat.Message',
        channel: c
    }).suchThat(j.not(messageIsRedacted));
}

function messageIsRedacted(m) {
    return j.exists({
        type: 'Chat.Message.Redacted',
        message: m
    });
}

j.watch(channel, j.for(messagesInChannel), displayMessage, removeMessage);

Continue With

for