1st Person Game Three.js - Controls - Moving the camera - three.js

Question

I want to create a 1st person 3D game with Three.JS. The controls are W A S D. I have the keys assigned to move forward (W), move backward (S), turn left (A) and turn right (D).
In this code I explain the logic behind the controls. The deltas' porpuse is to inform what direction the camera is looking, so that when it moves forward or backward it moves in that direction. That is what I'm having problems with.
//variables
var pi = Math.PI; //just because I use PI a lot
//controls
var moveForward = false;
var turnLeft = false;
var moveBackward = false;
var turnRight = false;
//direção
var deltaZ = pi;
var deltaX = 0;
var increaseDeltaX = true;
var increaseDeltaZ = false;
/*code adding the camera, the scene and eventListener for the keys. When the keys mentioned are clicked the corresponded var turns true*/
function animate() {
//clicking W
if (moveForward) {
camera.position.z += deltaZ/pi;
camera.position.x -= deltaX/pi;
//I used delta/pi because if delta=pi camera.position.z will increase 1
}
//clicking S
if (moveBackward) {
camera.position.z -= deltaZ/pi;
camera.position.x += deltaX/pi;
}
//clicking D
if (turnRight) {
camera.rotation.y += pi/300; //clicking 300 times will spin 180 degrees
//deltaZ starts in pi and decreasing, it varies between pi and -pi
if (increaseDeltaZ) {
deltaZ += pi / 150; //150= 300/2; pi= 90 degrees = 180/2
} else {
deltaZ -= pi / 150
}
if (deltaZ >= pi) {
increaseDeltaZ = false;
} else if (deltaZ <= -pi) {
increaseDeltaZ = true;
}
//deltaX starts in 0 and increasing, it varies between pi and -pi
if (increaseDeltaX) {
deltaX += pi / 150;
} else {
deltaX -= pi / 150;
}
if (deltaX >= pi) {
increaseDeltaX = false;
} else if (deltaX <= -pi) {
increaseDeltaX = true;
}
}
This code works well. When I turn right and then move forward, the camera moves in the right direction. The problem is when I turn the camera left. I tried to just reverse the calculations but the values just get messed up and the deltas go over pi and the directions become incorrect.
What do I put in the if (left)?