Unkown Identifier: 'Math'.

Im trying to get a random GameObject to spawn based off of what value is pulled from my array. But Untiy is returning the error “Assets/SpawnScript.js(27,39): BCE0005: Unknown identifier: ‘Math’.”
This is my code:

var powerUp = [‘FireSpeed’,‘Movement’,‘SlowTime’];

function PowerUp()
{

var rand = powerUp[Math.floor(Math.random() * powerUp.length)];  

if (rand === 'FireSpeed') 

{  
	Instantiate(fireSpeed, transform.position, transform.rotation);  
	GetComponent.<Rigidbody2D>().AddForce(transform.up);  
}  

if  (rand === 'Movement')  
{  
	Instantiate(movement, transform.position, transform.rotation);  
	GetComponent.<Rigidbody2D>().AddForce(transform.up);
}
if (rand === 'SlowTime')
{
	Instantiate(slowTime, transform.position, transform.rotation);
	GetComponent.<Rigidbody2D>().AddForce(transform.up);		
}

}

The unity math library can be referenced with Mathf keyword but it does not contain the Random functionality.

This one does.