expression-parser

An expression evaluator written in typescript with the goal to support SQL like WHERE clauses.

Installation

npm install --save @abdullah2993/expression-parser

Supported Operations and Functions

Arithmetics

• +
• -
• *
• /

Comparison

• =
• <>
• >
• >=
• <=

Logical

• and
• or

SQL

• IS NULL
• IS NOT NULL
• BETWEEN [NUMBER] AND [NUMBER]
• CASE WHEN expression THEN expression [WHEN expression] [ELSE expression] END

Functions

Currently only function that is evaluated is the LENGTH(variable) function but supports function calls at the parser level so it is fairly easy to add more SQL functions.

Examples

/** Basic Math **/evaluate('1+2'));// 3evaluate('10 + 2 * 6'));// 22evaluate('100 * 2 + 12'));// 212evaluate('100 * ( 2 + 12 )'));// 1400evaluate('100 * ( 2 + 12 ) / 14'));// 100/** Basic Math With Variable Substitution**/constcontext={a: 1,b: 2,c: 10,d: 6,e: 100,f: 12,g: 14,};evaluateObject('a+b',context));// 3evaluateObject('c + b * d',context));// 22evaluateObject('e * b + f',context));// 212evaluateObject('e * ( b + f )',context));// 1400evaluateObject('e * ( b + f ) / g',context));// 100/** Other Operations **/constval: any={a: null};evaluateObject('a is not null and length(a) between 4 and 10',val);// falseconstval={a: '123'};evaluateObject('a is not null and length(a) between 4 and 10',val);// falseconstval={a: '1234'};evaluateObject('a is not null and length(a) between 4 and 10',val);// trueconstval={a: '1234567890'};evaluateObject('a is not null and length(a) between 4 and 10',val);// trueconstval={a: '12345678901'};evaluateObject('a is not null and length(a) between 4 and 10',val);// falseconstval: any={a: 1,b: 1};evaluateObject('a is not null and b is not null',val);// trueevaluateObject('a is not null and b is null',val);// falseconstval={a: 1,b: null};evaluateObject('a is not null and b is null',val);// trueconstval={a: 1,b: 1};evaluateObject('a=b',val));// trueevaluateObject('a>b',val));// falseevaluateObject('a<b',val));// falseconstval={a: 1,b: 2};evaluateObject('a=b',val);// falseevaluateObject('a>b',val);// falseevaluateObject('a<b',val);// trueconstval={a: 1,b: 3};evaluateObject('case when a > 1 then true else false end',val);// falseconstval={a: 2,b: 3};evaluateObject('case when a > 1 then true else false end',val);// trueval={a: 2,b: 3};evaluateObject('case when a = 1 then 1 when a = 2 then 1 else false end',val);// 1evaluateObject('case when a = 1 then 1 when a = 2 then 2 else 3 end',val);// 2evaluateObject('case when a = 1 then 1 when a = 3 then 3 else 2 end',val);// 2construle=`case when light = 'Green' then 'Go' when light = 'Yellow' then 'Should Stop' when light = 'Red' then 'Stop' else 'Invalid State' end`;val={light: 'Yellow'};evaluateObject(rule,val))// 'Should Stop'val={light: 'Green'};evaluateObject(rule,val))// 'Go'val={light: 'Red'};evaluateObject(rule,val))// 'Stop'val={light: 'Blue'};evaluateObject(rule,val))// 'Invalid State'

Sample AST

//Expression: a is not null and length(a) between 4 and 10
{
"operator": "and",
"left": {
"operator": "<>",
"left": {
"name": "a",
"type": "IdentifierExpression"
},
"right": {
"value": null,
"type": "ValueExpression"
},
"type": "BinaryExpression"
},
"right": {
"operator": "and",
"left": {
"operator": ">=",
"left": {
"name": "length",
"args": [
{
"name": "a",
"type": "IdentifierExpression"
}
],
"type": "FunctionCallExpression"
},
"right": {
"value": 4,
"type": "ValueExpression"
},
"type": "BinaryExpression"
},
"right": {
"operator": "<=",
"left": {
"name": "length",
"args": [
{
"name": "a",
"type": "IdentifierExpression"
}
],
"type": "FunctionCallExpression"
},
"right": {
"value": 10,
"type": "ValueExpression"
},
"type": "BinaryExpression"
},
"type": "BinaryExpression"
},
"type": "BinaryExpression"
}

Test Coverage

13 specs, 0 failures
Finished in 0.069 seconds
Randomized with seed 62175 (jasmine --random=true --seed=62175)
--------------|---------|----------|---------|---------|-----------------------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
--------------|---------|----------|---------|---------|-----------------------------------
All files | 93.24 | 83.33 | 92.73 | 93.19 |
ast.ts | 89.66 | 100 | 90 | 90 | 16-18
evaluator.ts | 85 | 69.23 | 100 | 84.21 | 14,18,27,47-49,64
lexer.ts | 99.04 | 98 | 100 | 99.03 | 86
parser.ts | 89.89 | 70 | 89.47 | 89.41 | 83,91,103,121,133,137,144,181,184
token.ts | 97.06 | 100 | 75 | 96.97 | 44
--------------|---------|----------|---------|---------|-----------------------------------