dl-math-exp-string-eval

Math Expression String Evaluator

This is an Angular library which provides a service for evaluating mathematical expressions of string type and return a number. This library does not use the eval function which is a built-in JavaScript utility. This library was generated with Angular CLI version 7.2.0.

Note: All import statements within this sample code or elaborated in this document will either include projects/math-exp-string-eval/src/public-api or d depending on how the library was installed. Refer to Installation.

Documentation

To view the documentation, open doc/index.html. The documentation was generated using Compodoc tool. Compodoc is a useful tool for generating documentation for your Angular applications.

Installation

Using NPM

To install the library using npm:

npm i dl-math-exp-string-eval

This installation will include the import statement:

// For module import in app.modeul.ts
import { ExpMathStringEvalModule } from '../../node_modules/dl-math-exp-string-eval';

// For service import in component
import { ExpMathStringEvalService } from '../../node_modules/dl-math-exp-string-eval';

Manual

If you have cloned this repository and wish to use the library without installation through the Node Package Manager, then you can build the library by running:

ng build math-exp-string-eval

This will generate a module in dist directory by the name math-exp-string-eval. To manually add the library to your application, copy directory dist/math-exp-string-eval, in this repository, to your application's dist directory. In case if your application directory does not have a dist directory then create one. The import statements will include:

// For module import in app.modeul.ts
import { ExpMathStringEvalModule } from 'math-exp-string-eval';

// For service import in component
import { MathExpStringEvalService } from 'math-exp-string-eval';

Library Import

In the app.module.ts (or any module configuration) add ExpMathStringEvalModule to the imports array int @NgModule decorator. Then add the following line in the imports section of the module file:

import { ExpMathStringEvalModule } from  'projects/math-exp-string-eval/src/public-api';

This is for the case when the library is present within the projects directory. In case if the library is within node_modules, then make the changes accrodingly.

Description

The library evaluates a string expression through:

1. Tokenizing - A token can be a number, an operator, opening or closing parenthesis or a function name.
2. Evaluating unary operations - Expression of the type (-n) where n is a whole number are evaluated next.
3. Evaluating functions - Functions can be included in the expression and they are evaluated next.
4. Evaluating final native expression - A native expression is one where there are no functions or unary operations existing within the expression.

Token

A token represents an independent entity of the expression which has a unique purpose within the expression. There are seven types of tokens: Operator, Operand, OpenParenthesis, CloseParenthesis, DecimalPoint, FunctionName and Comma. Of these only DecimalPoint and Comma will not be tokenized into individual tokens. A token is represented by the DMEToken class which has the following:

Field	Type	Description
type	enum - TokenType	Specifies the type of token from the TokenType enum.
value	any	The value of the token, for a number the value is the value of the number.

Function

A function can be used within an expression provided it is defined within an object of type any and passed in the second paremeter of the evaluating methods. A function takes the form f1.f2...fn(param1, param2,..., paramN).

Usage

1. Configuring App Module

Import the module into app.module.ts. If the library is in dist directory then use:

import { ExpMathStringEvalModule } from 'math-exp-string-eval'

But if the library is within node_modules, installed using npm then use:

import { ExpMathStringEvalModule } from '../../node_modules/dl-math-exp-string-eval'

Add ExpMathStringEvalModule to the imports array in the @NgModule decorator of the application module file (usually named app.module.ts inside app component directory). A sample @NgModule decorator should look like this:

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    ExpMathStringEvalModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})

Once app.module.ts is configured, the service can now be injected into your components.

2. Service Injection

To use the service within a component (or wherever necessary), the service has to be injected into that component. A sample code for injecting the service into the app component:

<other imports>
import { ExpMathStringEvalService } from 'math-exp-string-eval';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})

constructor(private ser : ExpMathStringEvalService) { }

The above code injects the service into the constructor of the app component.

Demo

Run ng serve in this application and open the developer console to view the results. The demo code is present within app.component.ts. This application takes an expression in a string and the service is injected in the constructor in app.component.ts. There is an object which contains functions which are passed into the second argument of the evaluator method. Finally, there is invocation of the Math.sin method which is not defined in the list function, this is to demonstrate the look up which the service performs on the Math object of JS's library.

To run the demo, first build the library:

ng build math-exp-string-eval

and then run the application using Angular CLI's tool:

ng serve