phaser/examples/physics/angle between.js

var game = new Phaser.Game(800, 600, Phaser.CANVAS, 'phaser-example', { preload: preload, create: create, update: update, render: render });

function preload() {

    game.load.image('arrow', 'assets/sprites/longarrow.png');
    game.load.image('ball', 'assets/sprites/pangball.png');

}

var arrow;
var target;

function create() {

    game.stage.backgroundColor = '#0072bc';

    arrow = game.add.sprite(200, 250, 'arrow');
    arrow.anchor.setTo(0.1, 0.5);

    target = game.add.sprite(600, 400, 'ball');
    target.anchor.setTo(0.5, 0.5);
    target.inputEnabled = true;
    target.input.enableDrag(true);

}

function update() {

    arrow.rotation = game.physics.angleBetween(arrow, target);

}

function render() {

    game.debug.renderText("Drag the ball", 32, 32);
    game.debug.renderSpriteInfo(arrow, 32, 100);

}