StringGetIndexProperty.jsā¢1.31 kB
'use strict';
var callBound = require('call-bound');
var $TypeError = require('es-errors/type');
var $charAt = callBound('String.prototype.charAt');
var isString = require('is-string');
var isNegativeZero = require('math-intrinsics/isNegativeZero');
var unbox = require('unbox-primitive');
var CanonicalNumericIndexString = require('./CanonicalNumericIndexString');
var IsInteger = require('./IsInteger');
var isPropertyKey = require('../helpers/isPropertyKey');
// https://262.ecma-international.org/6.0/#sec-stringgetindexproperty
module.exports = function StringGetIndexProperty(S, P) {
if (typeof S === 'string' || !isString(S)) {
throw new $TypeError('Assertion failed: `S` must be a boxed String Object');
}
if (!isPropertyKey(P)) {
throw new $TypeError('Assertion failed: `P` must be a Property Key');
}
if (typeof P !== 'string') {
return void undefined;
}
var index = CanonicalNumericIndexString(P);
if (typeof index === 'undefined' || !IsInteger(index) || isNegativeZero(index)) {
return void undefined;
}
var str = unbox(S);
var len = str.length;
if (index < 0 || len <= index) {
return void undefined;
}
var resultStr = $charAt(str, index);
return {
'[[Configurable]]': false,
'[[Enumerable]]': true,
'[[Value]]': resultStr,
'[[Writable]]': false
};
};