Shader

Questions
1 
            // VERSION 4 - traditional GLSL 1 format (note version param in Shader)
            const fragment2 = `
void main() {
    gl_FragColor = mix(vec4(1,1,0,1), vec4(0,1,1,1), gl_FragCoord.x/iResolution.x);
    vec2 fragCoord = gl_FragCoord.xy;
    vec4 t = texture(iChannel0, fragCoord.xy/iResolution.xy);
    gl_FragColor = vec4(t.g, t.b, t.r, t.a);
}
`;
            const shader2 = new Shader({
                width: 200,
                height: 200,
                fragment: fragment2,
                version:"",
                channel0: obj.clone()
            }).pos(250, 0, CENTER, CENTER).drag();

i use VERSION 4 - traditional GLSL 1 format fragment,can't show the shader.
where is the problem ?