WebGL- Sending textures from JS to shader- problems

I literally have no idea what I need to do to fix the code- I’m trying to send color information from javascript to webgl via shaders- I have a showing program- I basically want (at this point) to be able to print out my shader onto the screen, but all it does it show black :confused:

IN javascript:

            var count=0;
            var table = new Float32Array(128*4);
             for (var y = 0; y<(128*4); y+=1) {

                 var sig = .35;
                 table[count++] = sig;
                 table[count++] = sig;
                 table[count++] = sig;
                 table[count++] = 1;

            texturetab = gl.createTexture();
            gl.bindTexture(gl.TEXTURE_2D, texturetab);
            gl.pixelStorei(gl.UNPACK_ALIGNMENT, 1);
            gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 128*4, 1, 0,
                          gl.RGBA, gl.FLOAT, table);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
            //irrelevant code taken out for conciseness
            gl.uniform1i(gl.getUniformLocation(prog, "uTabSamp"), 2);

Fragment Shader:

 uniform sampler2D uTabSamp;
        const float d = 0.001953125; // 1./512. our delta (finite difference)
        void main(void) {
             sigmoid = texture2D(uTabSamp, vec2(2.5/128. ,.5)).r;

            //irrelevant code taken out

            gl_FragColor = vec4(texture2D(uTabSamp, vec2(3.0/128. ,.5)).r, 0,0,1. );


Basically, I want to see that I’m at least getting some output on the screen from the texture- all I get is a black screen, though…