How to set a time uniform in webgl

I am new to webgl. I am trying to set a time uniform, so I can change the output of my fragment shader as time passes. I thought this would be fairly simple to implement but I am struggling. I am aware that these two methods are probably involved:

• https://developer.mozilla.org/en-US/docs/Web/API/WebGLUniformLocation

• https://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/uniform

Is some kind of rendering loop required?

Any help here would be really appreciated, thanks.