Using ThreeJs, is there any way to limit x, y z movement? - three.js

Question

In ThreeJS, I am using firstpersoncontrols to move the camera around; I would like to set a limit (max and min) in which the viewer can move in the x and z direction. Is there are property that I can use?
Currently I have tried amending code in the firstPersoncontrols.js, though the effect is not wonderful:
var targetPosition = this.target,
position = this.object.position;
var maxx = Math.sqrt(Math.pow(6000,2) - Math.pow(position.z + 100 * Math.sin( this.phi ) * Math.sin( this.theta ) + 500,2)) - 500;
var minx = - Math.sqrt(Math.pow(6000,2) - Math.pow(position.z + 100 * Math.sin( this.phi ) * Math.sin( this.theta ) + 500,2)) + 500;
var maxz = Math.sqrt(Math.pow(6000,2) - Math.pow(position.x + 100 * Math.sin( this.phi ) * Math.cos( this.theta ) - 500,2)) - 500;
var minz = - Math.sqrt(Math.pow(6000,2) - Math.pow(position.x + 100 * Math.sin( this.phi ) * Math.cos( this.theta ) - 500,2)) + 500;
if (position.x + 100 * Math.sin( this.phi ) * Math.cos( this.theta ) <= maxx && position.x + 100 * Math.sin( this.phi ) * Math.cos( this.theta ) >= minx) {
targetPosition.x = position.x + 100 * Math.sin( this.phi ) * Math.cos( this.theta );
} else {
position.x = position.x - 100 * Math.sin( this.phi ) * Math.cos( this.theta );
targetPosition.x = position.x;
}
targetPosition.y = position.y + 100 * Math.cos( this.phi );
if (position.z + 100 * Math.sin( this.phi ) * Math.sin( this.theta ) <= maxz && position.z + 100 * Math.sin( this.phi ) * Math.sin( this.theta ) >= minz) {
targetPosition.z = position.z + 100 * Math.sin( this.phi ) * Math.sin( this.theta );
} else {
position.z = position.z - 100 * Math.sin( this.phi ) * Math.sin( this.theta );
targetPosition.z = position.z
}
this.object.lookAt( targetPosition );

Answer 1

Ultimately the question was aimed at persons familiar with the first person controls in the threejs library.
I was wanted to place a max and min value to x and z, to prevent the user/camera moving to far in either direction; the solutions that I found (the one above and a later improved version) were not sophisticated, and resulted juddering and other problems.
Eventually, I removed firstpersoncontrols from the code, and used a path instead, so that the user would be automatically guided around the 3D space. this was not ideal, I would have preferred the user to guide their self, but with boundaries to stop them straying to far from the defined scene.