These define the shadow map types used by the WebGLRenderer.
THREE.BasicShadowMap
Unfiltered shadow maps - fastest, but lowest quality.
THREE.PCFShadowMap
Shadow maps filtered using the Percentage-Closer Filtering (PCF) algorithm (default).
THREE.PCFSoftShadowMap
Shadow maps filtered using the Percentage-Closer Soft Shadows (PCSS) algorithm.
var renderer = new THREE.WebGLRenderer();
renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFShadowMap; //default
Note that this just enables shadows in the renderer and sets the shadow map type.