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TypeScript - float regular expression
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In this short article, we would like to show how in a simple way check if the text is a float number using regular expressions in TypeScript.
Quick solution:
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const expression: RegExp = /^[+-]?(?:\d+(?:\.\d*)?|\.\d+)(?:[eE][+-]?\d+)?$/;2
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const isFloat = (text: string): boolean => !!text.match(expression);4
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// Usage example:7
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console.log(isFloat('123')); // true9
console.log(isFloat('3.14')); // true10
console.error(isFloat('abc')); // false11
console.error(isFloat('a123b')); // false
Example in this section prints error messages only when incidated number is incorrect.
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const expression: RegExp = /^[+-]?(?:\d+(?:\.\d*)?|\.\d+)(?:[eE][+-]?\d+)?$/;2
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// Where:4
// ^ <- text matching since begining5
// [+-]? <- optional sign before float number e.g. + or -6
// (?:\d+(?:\.\d*)?|\.\d+) <- integer number, e.g. 1237
// or integer number with dot between, e.g. 0.1238
// or integer number with dot before, e.g. .1239
// or integer number with dot after, e.g. 123.10
// (?:[eE][+-]?\d+)? <- e or E with optional sign and integer number11
// e.g. e10, E10, e-10, E-10, e+10, E+1012
// $ <- text matching up to ending13
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const isFloat = (text: string): boolean => !!text.match(expression);15
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// Testing section (printing only if error detected):18
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const values: string[] = [20
'123', '-123', '+123', // integer numbers21
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'123.0', '-123.0', '+123.0', // optional sign + integer number with dot between23
'0.123', '-0.123', '+0.123', // optional sign + integer number with dot between24
'3.141', '-3.141', '+3.141', // optional sign + integer number with dot between25
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'.123', '-.123', '+.123', // optional sign + integer number with dot before27
'123.', '-123.', '+123.', // optional sign + integer number with dot after28
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'0.1e10', '0.1e-10', '0.1e+10', // scientific notation with e30
'0.1E10', '0.1E-10', '0.1E+10' // scientific notation with E31
];32
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for (const value of values) {34
if (!isFloat(value)) {35
console.log(`${value} is not compatible with float number!`);36
}37
}