These work with all material types. First set the material's blending mode to v3d.CustomBlending, then set the desired Blending Equation, Source Factor and Destination Factor.
const material = new v3d.MeshBasicMaterial({color: 0x00ff00});
material.blending = v3d.CustomBlending;
material.blendEquation = v3d.AddEquation; //default
material.blendSrc = v3d.SrcAlphaFactor; //default
material.blendDst = v3d.OneMinusSrcAlphaFactor; //default
v3d.AddEquation
v3d.SubtractEquation
v3d.ReverseSubtractEquation
v3d.MinEquation
v3d.MaxEquation
v3d.ZeroFactor
v3d.OneFactor
v3d.SrcColorFactor
v3d.OneMinusSrcColorFactor
v3d.SrcAlphaFactor
v3d.OneMinusSrcAlphaFactor
v3d.DstAlphaFactor
v3d.OneMinusDstAlphaFactor
v3d.DstColorFactor
v3d.OneMinusDstColorFactor
v3d.SrcAlphaSaturateFactor
All of the Source Factors are valid as Destination Factors, except for v3d.SrcAlphaSaturateFactor
For more info on how to obtain the source code of this module see this page.