test-client-invoke.js

const  AWS = require('aws-sdk');

var params = {
        IdentityPoolId: "ap-southeast-1:xxxx" 
};
 AWS.config.region = 'ap-southeast-1';
 AWS.config.credentials = new AWS.CognitoIdentityCredentials(params);

var lambda = new AWS.Lambda();
lambda.invoke({
    FunctionName: 'client-lambda-dev-public', // your function name
    Payload: JSON.stringify({}) // how you send the email to the Lambda event
}, function(err, data){
    if (err) {
        console.log(err, err.stack);
    } else {
        console.log(data);
    }
});