NewChatGui.js

var ASMAPI = Java.type("net.minecraftforge.coremod.api.ASMAPI");
var Opcodes = Java.type("org.objectweb.asm.Opcodes");

var InsnList = Java.type("org.objectweb.asm.tree.InsnList");
var MethodInsnNode = Java.type("org.objectweb.asm.tree.MethodInsnNode");
var VarInsnNode = Java.type("org.objectweb.asm.tree.VarInsnNode");
var IntInsnNode = Java.type("org.objectweb.asm.tree.IntInsnNode");
var InsnNode = Java.type("org.objectweb.asm.tree.InsnNode");

var RENDER = ASMAPI.mapMethod("func_146230_a");
var ENABLEBLEND = ASMAPI.mapMethod("enableBlend");

function initializeCoreMod() {
    return {
        "craftcord NewChatGui transformer": {
            "target": {
                "type": "CLASS",
                "name": "net.minecraft.client.gui.NewChatGui"
            },
            "transformer": function(classnode) {
                classnode.methods.forEach(function(method)  {
                    if (method.name === RENDER) {
                        patchRender(method.instructions);
                    }
                });

                return classnode;
            }
        }
    };
}

function patchRender(instructions) {
    var targetNode;

    for (var i = 0; i < instructions.size(); i++) {
        if (instructions.get(i).getOpcode() === Opcodes.INVOKESTATIC && instructions.get(i).name === ENABLEBLEND) {

            targetNode = instructions.get(i);
            print("found!");
        }
    }

    var toInsert = new InsnList();

    toInsert.add(new VarInsnNode(Opcodes.ALOAD, 22));
    toInsert.add(new VarInsnNode(Opcodes.ILOAD, 21));
    toInsert.add(new IntInsnNode(Opcodes.BIPUSH, 8));
    toInsert.add(new InsnNode(Opcodes.ISUB));
    toInsert.add(new InsnNode(Opcodes.I2F));
    toInsert.add(new MethodInsnNode(
        Opcodes.INVOKESTATIC,
        "com/karelmikie3/craftcord/patch/NewChatGuiPatch",
        "addEmotes",
        "(Ljava/lang/String;F)Ljava/lang/String;",
        false
    ));
    toInsert.add(new VarInsnNode(Opcodes.ASTORE, 22));

    instructions.insert(targetNode, toInsert);
}